A good year or so ago I installed a dual band (VHF/UHF) antenna through the roof. If you don't know what these are, this probably won't apply to you much, but if you do know, then you may find this valuable.

Talk about sweating it out when I put the drill bit on the roof!!

This is the style I bought:


Anyway, I've been having issues keeping it tight and with the whip hitting drive through signs, etc. I started noticing it was angled back about two degrees or so, and I was having to continually tighten down the collar. Once it was so loose it leaked.

The mount base is small (so it will fit through the hole you drilled). Anyway, it only has maybe a little over 1/4" width, so not much to 'bite' the roof with.

I played around and found that the metal plates that go over household duplex power boxes (the kind you'd find in your garage)...those holes in the middle are the same size you drill for the mount.

A little bit of cutting on the plastic liner that holds the roof console and the rear AC controls, and it slipped in perfect. We are in the middle of a good rain event here, not a single drop of water in and the antenna sits straight.

I'll add some pics after the rain stops!

 

Looking forward to the pics Robert, I'm interested to see this.
I have had up to three mag mount antennas (antenni ? ) on my EX for a CB and a few scanners, I've never got up the nerve to drill my roof though, I've done it on Fire Dept vehicles in the past and they turned out fine but so far I'm chicken to do my own NMOs.

 

Here's one:


So the install was easy...the rear AC control panel pops out...the front end has two snap type connectors, the back side has two long tabs that just go into slots in the roof console mount. You can start pulling it off from the back just to get your fingers in, but slide them to the front and pop the connectors out there so you don't inadvertently break the rear tabs off.

I used a hole saw to cut through the plastic console mount. I used one with the shortest bit I could find and luckily that didn't also go through the roof. That's what made the circular hole you see in the middle.

Once I had a hole and room to work, I used a step bit for the next part. I don't recall what the size was, but it's the same size as the center hole of a double-gang electrical box cover.

You can't see it in the first pic, so here is a similar design of the mount...there isn't much for the mount to actually grip on the underside of the roof:


Any pressure on the sides that don't have anything to grip will flex the roof...too much pressure on the sides that do grip will bend the metal of the roof.

My fix was to put a 2nd layer of thicker metal on the inside of the roof. This would provide a stiffer plate that would limit flex (distribute the pressure over a larger area than the NMO mount by itself could do), and to give me a future option to seal it if any more water comes in.

Be sure to get one that either a) has the correct size center hole pre-punched so you can just pop it out with a screwdriver or b) one with no hole at all and drill your own. They do sometimes come with different size holes depending on the size conduit that would connect to it.

After popping the center hole out of the gang plate cover, the problem was how to get the plate between the roof and the console mount.

I first cut a slot on the rear part of the console mount and slipping it in, then I realized I couldn't get my hands in to pull it forward into place.

A little more thought and I realized I could just cut away a triangular shaped piece away with no issues, and that would let me keep a grip on it while I slipped it in to the rear and pulled it forward.

Tricky part - you have to have someone keep the NMO mount base in place, centered from the inside while you tighten the collar screw from the outside. My wife struggled (on the inside half) a bit but after a few tries we got it tightened down.

Pleased to report that after over an inch of rain the mount is still bone dry. I may revisit it in the summer (when the roof starts to take a beating from the sun) and verify everything is still tight and possibly add sealant if it isn't.

 

Thanks for the pic and description, I still don't know if I'll get up the nerve to do this just yet. I know that I should, it will help with reception and look so much cleaner than having the cables snaking around door seals but......... I'm chicken.

 

I have a light bar on the roof and when we convoy I sometimes run a 2nd mag mount for our tac radios. I haven't found a good quick-disconnect for the light bar, so drilling a 2nd hole isn't a solution.

I also hated the "hope I don't pinch the feed line in the door" route, so I've taken to running the feed line to the back of the truck (just inside the roof rack track), then through the larger opening of the rear hatch, then through the vent at the top of the roof. I cut small sections of 1" wide aluminum flat bar and made clips to keep the feed line from flapping all over the roof. You can use the flat nuts from a wrecked truck (Excursion...and the Expedition might also be the same size), or you can just thread another small section of the same aluminum bar. Drill two small holes through the clip and you can zip tie the feed line to keep it in place.

From the side you can't see the feed line as it is blocked by the roof rack track. You can see just a tiny bit where it goes into the hinge of the back hatch, but it (IMO) looks much cleaner than through the side doors, and best of all no chance to really pinch the line and damage it.