What would be the best method of mounting a flatbed on my pickup frame?

I haven't built it yet so I have 2 options.

A) Parallel beams running along the frame with hardwood shimming the frame up so it's flat.

B) Running 'C' channel across (right angle to the frame) in 5 or 6 places (would need different widths) running the bed supports parallel to the frame.

I would prefer 'A' but I don't know if it would be prohibitively difficult, or be weaker than option 'B'.

The reasons I am replacing the factory bed:
-The P.O. put an "Inverted 5th Wheel" hitch in my truck and cut a very large hole in the center of the bed to do so. I cannot use this hitch so it has to go, leaving behind a large hole. It is also welded to the frame.
-There are 2 roughly 6" holes in the floor near the front for a stack. One (in use) inside the frame rail, one (really rough cut and mostly square) on the outside of the frame rail. Both are on the pass. side.
-The bed floor is 'wavy' from repeated abuse(?) and the bed front is bent forward to within 1/2" of the cab.

Thank you for all the advice you guys have given. Sorry for such a long post.

 

A definately.

 

While i agree Star, what is your reasoning? Stronger? More open as far as designing?

I'm also planning on using side plates to secure the bed to the frame.

 

Stronger and tire clearance, plus it is easier. I always built them and tacked them together right on the pickup. Oh and side plates work great, I usually run the two channels first and either use plates or ubolts to secure the wood too.

 

Currently the end of my bed is 39" from the ground. If the end of the new bed is 46-48" from the ground, is this going to be too high to pull a gooseneck or 5er?

I'm going to build a lower receiver for pulling tags.

 

I've got flatbed experience with the cab and chasses frames, but no pickup experience. Do you have a picture of the frame? I know they aren't as flat as the cab and chassis, which makes it harder to mount beds to.
You might consider a hybrid of your "A" and "B" options. Run some 4" C-Channel the length of the frame, with hardwood underneath to shim up the low spots. Then run your perpendicular beams across that. Space the beams closer for maximum strength. Run more than you think you need, then you'll know you're good! Mount your deck on top and call it good.
Have you skipped the idea of wood and are stuck on steel? My wood flatbed is 10' long x 7' 8" wide, the perpendicular beams are 2x8's each ripped a different width to compensate for the sligth bumps on the cab and chassis frame. (I'm going to replace them with 2x12's screwed together to be 4x12's to gain some height for the fuel hose) The bed has fold-down sides with steel 4" hinges. I can fit about 70 square bales of hay with the sides folded down. It's also light-weight, medium duty, easy to repair, and cheap to build ($100 of lowe's lumber). My uncle's a carpenter, and he said the bed will stand up to anything but fire. Well, except for the fold-down sides, they can't take too much weight against them...until I fabricate some better hinge setup.
Your biggest obstacle is the fuel filler neck! If you don't plan on having the bed dump, then you'll need to mount the entire bed high on the frame. Why? To maximize the slope of the fuel filler neck. My bed is 8" taller than my truck frame, with the fuel filler hose almost flat. Not good enough. Even with a big oversized vent, the thing fills up VERY slow and spills about a 1/2 gallon of fuel at every fill-up. Plan on having the fuel filler hose as high up as possible, which means building the bed tall with your beams. This will also be beneficial if you load the truck up, your tires won't rub if the bed is tall.
If you're interested I'll take pictures of my bed, fuel filler setup, and the perpendicular beams tomorrow in the daylgith after school. Even if you're not interested in wood, it'll give you an idea of what I mean about the fuel hose.

 

One concern with wood is i eventually want a 5th wheel and gooseneck hitches.

Also, any word on the bed being too high for a goose or 5er at 46-48"?

 

True! The wood won't work for that. I don't have any gooseneck or 5th wheel experience, so I can't help you with the height.

 

lots of guys here in fl run flat beds with 5th wheels and goosenecks with no problems what state are you from

 

Here is a bed that I built a few years ago that is pretty versatile. It has a hidden goosneck ball with a 1 foot by 1 foot door on hinges to close when not in use. the electrical connections for it and the fifthwheel is also in there. I built a mount to where with an impact I can mount the fifthwheel by myself in less than 10 minutes. There is flush mount standards made out of square tubing that I have some 18" side boards that just slide in. I have an 18" extension that pins on the back for when hauling hay or anything you need a 10 foot bed for, it is covered with diamond shaped expanded metal so you can fold it down and still see the liscence plate and lights, and if you fold it up it is the tailgate if I have my side boards on. The four built in boxes lock, but the one on the passenger back is not as big as it looks because it has a heavy wall 4" pipe through it that a hydraulic crane slides into wheh I need to load something heavy. I recessed the lisence plate two inches so it doesn't get damaged when hooking on to a trailer and the plate light too. The bumper is a 2 x4 heavy wall tube laid flat so it only stickes out 4" and makes a good step to get on the bed. All the lights are flush mount sealed beam truck lights including the backup lights. The fuel necks are recessed and right at the top of the bed but I screwed up here, the bed needs to be 1 to 2" higher, some pumps you can run wide open but a lot of them you have to baby it filling it up. I will fix this when I swap cabs. I plan on raising the body so I can raise the bed 1" and it will still look right.
It is 3 1/2 inches wider than the cab on each side so if a guy wanted stacks they would look pretty good mounted to the front of the bed.



You can see the hinges for the extension here and the reese hitch only sticks out 1/2 inch.

You can kinda see how I recessed the fuel necks here.

This bed took awhile to build, but I wanted it to be versatile, if it was 1" higher and dumped it would be perfect. lol

 

Fast, I'm from IN. It's not that i'm worried about being allowed to pull a goose, i'm concerned about my bed being too high for the trailers...

Star, looks good. My main concern is written above ^.

 

what do you mean too high for trailers?

 

46 inches is going to be pretty high for a 5er and if you don't have an adjustable neck on a goosneck it will be pretty high there too. That is the reason besides I'm lazy and it is easier to load a low bed, that I built this bed so low, When I was running the shop and wrecker service I never knew what I was going to need to pull. That is actually why I built my own mount for the 5ver hitch was to keep it low. Is your truck lifted or what.

 

The only way I can think to make it low enough is to use option B from my original post.

***thinking out loud here***

I measured from the ground to the highest part of the frame and it was 35". If i use a 3" main beam and 2" cross beams that will put me at 40". While 1" higher should be fine, will 2" channel on 20" spacings be strong enough?

If I switch to option B, building similar to this member's bed, that will put the height at 38". 1" lower than stock. The problem I see with building like in the link is that my frame only has 8 holes, not 10, so I would still have to find a way to use side plates. Also, would the design in the link be strong enough to pull a 15K goose/5er/tag? (not that i need to, just don't want to under build it)

Another problem with Option B is that I want to exend the bed past the end of the frame and move it 1.5" farther away from the cab.

P.S. Maybe i should mention that all of my measurements from the ground are sitting on 35" rear tires and 33" front tires. Before I start towing I'm switching back to the stock 235/85, which are 32". Will this lower all of my rear measurements by 3"? If yes then i could use my 4" mains and 3" crosses putting the end of the bed at 39". Back where I'm at now.

Once I get all of this ironed out I'll post up my design for final advice.

You guys are a bunch of help. Thank you much!

 

If you run them crossways use angle iron to mount them to the frame. where are you going to mount your fuel fillers.