I thought I'd contribute to this Forum as I do within my many other Boards. This is a pretty easy mod (but I'll step it out as easy as I can, cuz I know... as soon as I don't? hehe). As always, morph off of this as you see fit for your situation.
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Some things you'll need:
--Weatherproof lockset; here's the $12.77 lock I used (I can see Black trucks maybe wanting an anodized black version?). The shank length has to be 1-1/2 to 1-3/4". Any longer and you will hit on pivoting/opening (of the fuel door) and any shorter you won't make the right side sill to latch. Suggest you inspect your inside fuel door, you'll then understand all of this.
--Power Drill
--3/4" holesaw w mandrel bit guide. Note! use a 1/64" bit for pilot hole prior, otherwise the mandrel bit will skate somewhat (+1-1/2 hole saw for Back panel additional modification *See Step 6)
--Dremel tool with narrow cutting disc (or a mandrel drill set as pictured)
--Marking pen, you can even use your wife's best red lipstick!

Please Note: There are 2 panels to the fuel door. The 'Front' (outside painted) visual side and the 'Back' (Inside-reinforcement) panel. These will be noted simply as: Front ||and|| Back panels. Do not mix the 2 up when drilling!.




1) 'Front' panel; center and mark hole for pilot drilling, do not go too close to the raised finger-lip as you will not have enough sweeping room for the latch or the lock stem itself when swinging door (on open & close).
2) Using your 3/4" diameter hole saw, drill through 'Front' (and 'Back' cover if NOT doing Step 6 mod) Note!*for 'Back' cover mod (see step 6); only pilot (by mandrel of the hole saw) the 'Back' panel (only) when drilling out the 'Front' side fuel door. This will act as a guide for the 1-1/2" Inner hole. If you drill out both the 'Front' and the 'Back' to 3/4", no biggie, you will just have to hand guide the 1-1/2" Inner hole without the mandrel hole as guidance.





3) Insert the lockset (from the 'Front') and hand tighten the rear stem nut, install swing latch bar.





4) On the bottom/right corner of the swing latch-bar, mark/blot-up this with something that will transfer (oil based making pen, lipstick etc) to where you will then Dremel out the slot for the latch-bar to lock into. This mark is important for a nice correct/tight fit. Marking the slot; Give a very gentle push-in on the Outside door when making this mark (by turning key so latch makes contact with right side sill). This will insure a correct location (start of) the slot for the latch. This is my initial rough cut shown (image), clean it up from here, just don't get it sloppy!.






5) [If you don't do the optional 1-1/2" 'Back' side cover hole] Observe and notice that if you over tighten, you will get a dimple-in effect right at the lock-set location. This is plastic, so I would advise this one more step below (your call)...






6) *Optional [TS1 recommended]. With the lock-set removed (image doesn't reflect this of course); using a 1-1/2" hole saw, drill out the 'Inner' fuel door (liner) to expose the locksets front 3/4" entry hole (but the backside of the course), be careful not to drill through or touch the 3/4' Outer hole (when drilling this backside liner). [note] You will now have a 3/4" hole on the Outer front fuel door, and a 1-1/2" hole on the Inside door panel. Before you put the (stem) nut on, install a 3/4" ID SAE washer first, this will add major stability to the lock-set. I would also recommend using locktite on this once you have the lock in place and tested. Vibrations happen!






7) If you want the super paranoia mod?... maybe include the Stant 10510D locking fuel cap, I got mine for $10.33 here
Sorry, at time of this writing, I do not have a DEF locking cap that works for our SD's.




Conclusion) This mod is not goon proof but it does work quite nicely. If you do the additional mod with the 3/4" ID SAE washer re-inforcing the backside of the lockset, I think you will be very happy. It's firm and secure!

Using the finger slot, you can apply a lot of pressure with no give whatsoever (noting it is a plastic door!). Now granted, a crow bar is another thing, but I think even just having the visual in place as a huge step forward in protecting our fuel or DEF sources form getting vandalized via contamination.

Choosing this lock-set^ it allows you to remove key in the unlocked position also (3 images above). This can be handy for mega Interstate refueling trips or where you just don't want a locked door, noting that the appearance will still be there!

My main reason for doing this mod was vandalism, possibly stopping some bored kids at a campsite from pouring down their Gatorade's into one of the tanks. Fuel siphoning I can deal better than several thousand$ in engine repair bills. So help protect your investment!?, and I hope this helps out within our community!

KJ & Debbie... and happy hour is always open at our campsite!... I'm guess'n like your average 5th wheel tow jockies!

 

VERY nice write up and instructions.

 

Great info. I'd be tempted to use a shorter (or shorten) bar on the lock and epoxy a catch for the lock instead of grinding a slot.

 

I don't think it would be nearly as secure, but you could do it externally on the catch.

Remember if it only catches on let's say 1/8" lip, that is very easy to pull (the door) and have the latch get bent/ bypassing the catch area.

Also keeping the lock shaft closest to the right latching point; secure critical. The caveat to this is you have to be able to "swing" that latch barrel beyond that right sill as well. I think my measurements above to be pretty close to the "sweet spot" for both security and functionality.

 

These locks are Cam Locks used a lot with boat cabinets. I have them on one of my Whalers. Be careful if you remove or switch the catch shaft as the whole lock mechanism can slide out of the screw barrel. The key indents will at that point end up on the floor with no hope of replacement. Don't ask me how I know this.

Thanks for the write-up. Interesting idea.

 

Thank you for nice write up and instructions. Had this on my 16' and going to do this on my 17'.. Very cheap insurance for sure...


Do you know where I can find it in black though as I think it would look better with my color combo?

 

Thanks guys, a cheap mod that just could save big someday, and most likely we'll never know!

The lock I used and suggested comes from the RV industry. It's used for an outside storage cabinet latch.

I know I suggested black for some trucks, but I never searched them. Since my door handles were chrome, I thought the silver lock matched up.

When you search, just make sure it's a weatherproof model, and has the little keyway door/cover.

 

Good job, I already have the start locking cap, and this looks smart to me. I don't want any interference with the DEF or my $300 worth of diesel.

 

Great idea! Now to figure out a power lock that works with the door lock/unlock....hummmmmm perhaps a use for one of my upfitter switches!

 

What about the DEF cap? Or is that not a concern.

I never thought of it but seems really easy just to open up a car or truck fuel cap and dump crap in there. Guess I take that for granted.

 

Yet another mod I've just got to have.... Thanks!

 

The DEF locking cap is a concern, but the blue one on Amazon that says it fits... doesn't.

I'm sure we will have several customers inline when we find a lockable DEF cap that works for us.

 

Good mod. Anyone else find their fuel door to feel very, very flimsy?

 

The CH751 Lock? I changed all my locks on my rv out from those as everyone in the world, especially if they have an rv, has that key. Id go with one of the round barrel key type locks.

 

Definitely not the key cut my prior Sunnybrook uses for it's storage bays. I also own a True Value hardware chain and have cut keys for over 25 years, so I know all about pin/depth cuts in keys.

Problem is w the round barrel type locks is...
-They are not weatherproof nor have the key slot protection door.
-Not very many pin-nub combinations, which means you will get redundancy very quickly. Our Soda machine "round key" also opens one of our lockable drill bit cases. Our router bit cabinet is also opened by another key ...forgot what that was doubled up with?, one of my employees told me a couple of Months ago. She thought she had a big surprise for me, lol... nope.

So anyone with a better weatherproof lockset solution fire away!! (I do like the solenoid, servo or relay triggered idea however!)