Actually, I see several problems with this in direct install experience...
Ok, the "seams" used to anchor, seal - fix the finish metal to the cab framework is not the best for RF.
@Recon - you covered your bases when you went the thru both the support brace and finish mount together - you kept the RF ground run and the electrical DC shield run pretty much congruous READ=EQUAL to each other so you kept the SWR and DC grounding conditions satisfied..
In fact, when it (vehicle) uses either standard sheet metal (treated) or the Aluminum - both will "perforate" under Tig and Mig welds simple due to the lack of real metal they offer - so you may be able to spot weld something in these newer exotic designs for a weld - but you're also going to find several problems related to the effort it will take to fix the repair if it tears or bead/molts (or Melts) away. (Kinda like a Plasma cutter torch) The conduction is stopped in many cases simply due to the nature of the Epoxy used to bond the finish metal to the seam crimps - they realize Galvanic and Electrolytic corrosion points are the very spot welds themselves. So they used an Epoxy glue instead...
I saw many vehicles come in our shop with some type of issue with operation of either the CB, Radio or amp or combo of all - and they used a bolt that they thought went to thru to the Frame.
Well in a way, it did work, as in at one time it provided the ELECTRICAL connection as well as the PHYSICAL - but they way these frames are seamed together - you start with a base, but only spot weld to hold brackets and cage parts until other pieces of the frame and finish metals are assembled.
Assembled is a term I used here because it means just that. It's (The vehicle body) is held together by the sum of all of it's parts. One part begins to fail may not be detrimental to the performance of the vehicle. However, It has the potential to be the problem you have when it comes down to finding out why a Seat-Belt bracket Bolt can't be ground. Wait until you see where the Bonding for Battery Ground is made, not to the undercarriage, but to the main chassis that holds the engine and drive train, (like those AWD or FWD "drop ins"). It then gets bolted to the vehicle thru a process of convoluted twisting and turning to "interlock" the "fingers" the engine chassis has to the "holes" the carriage has - fit the bolts in and tighten - you're done.
That means nothing to the electrical side of the problem. But, the Seat belt bolt is held onto the undercarriage and the undercarriage is pulled along by the drive train that bolted to the engine and it's motor mounts. Ok, so we got that, but remember the undercarriage is an assembly of all those spot welded and glued together parts like front pieces, side panels, center brace and rear panels and trunk. It's all spot welded and epoxy seamed together - and that key word here is spot welded. The Epoxy is strong enough to bear the loads and maintain integrity for a considerable number of years even exposed to the elements - and when painted over - can remain sealed until "Jarred" or otherwise deformed by collision. It's the Spot weld within this panel - when it fails - that will open the circuit you're trying to complete with any type of bolt or fastener used in that particular panel.
The vehicle - in it's lifetime - can lose spot weld points and remain intact because of the integrity of the design and the epoxy welding of the pieces - but that won't make very conductive Ground Points any more effective unless you're willing to chance the idea of bolting sections together by those seams. You obtain a bond point for ground, but you may lose the ability to keep corrosion from acerbating the degradation of the joint and lessening the integrity and shortening the life of the vehicle thru corrosion once you're bolting thru.
To put this point blank, the vehicle won't rust thru if the spot weld "pops" - but anything in that region of the panels' ground points bolted to that metal may not find ground shielding like the other panels. It's a proven problem in new cars, you can see this poor ground return issue in them. They will run ok, and seem to be alright but they behave differently. They have "odd" quirks and intermittent operation of sub-sections. Its' simply due to the fact that the ground used for that sub system and the ground point it expects to have for battery power return - is not there. The Spot weld and bolt aren't making contact to the vehicles ground buss anymore.
It is no longer a simple put the bolt thru and smash the lug, Star washer - nut 2 bolt and put panels together anymore - in fact there is a specific routing of wiring and the ground buss many newer vehicles uses as a method of shielding and taming common current and low-noise routings (CAN buss systems) in a honeycomb of various folds and seams designed to provide shielding from noises as well as protection from EMF/EMP problems of todays electronics to keep these sub systems from false triggering.
You don't want your Takatah-made Airbags to go off the first time you call "Break 19" - it may be your last time you're ever heard from...