Panel Boding Adhesive for Bed Crossmember / Sill Replacement?

[Jim_Philly]

Hey guys, I am preparing to remove the bed on my recently acquired '03 FX4 and replace 2 of the crossmembers/sills. The 2 rearmost ones are in good shape, and the front one near the cab is passable. The shorter, middle ones on either side of the wheel arches not so much. I managed to find an OEM crossmember for the rear one, but I'll need to get the front one fabricated.

Anyway, before I go down the welding path, I'm wondering if anyone with relevant experience can recommend for or against using 3m panel bonding adhesive to attach the new sills to the bottom of the bed floor? A couple of products I'm considering:

https://www.3m.com/3M/en_US/company-us/all-3m-products/~/All-3M-Products/?N=5002385+3293241847&preselect=7569132+8711017+3289697919+3294857497&rt=rud

https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Impact-Resistant-Structural-Adhesive-IRSA-/?N=5002385+8710676+8710693+8712771+3291264165&preselect=8709313&rt=rud

I figure absolute worst-case scenario, if the adhesive fails, there are still 6 bolts going through the frame and bed and I will notice it coming loose or rattling before anything catastrophic happens.

 

[Grumpaw]

Always thought about what I would use to bond two pieces of metal as I can't weld either. Especially if there are nuts/bolts holding it in addition.
Product called Roof Flashing Adhesive is what I'd use. Regular caulk tube, but the stuff is a thick black, almost rubbery stuff that doesn't fully harden...stays flexible and is 100% waterproof. Best part is that it is super sticky, like a super thick bonding caulk.
I used it starting in 2012 to seal all the outside gaps on our motorhome where outside compartments met the side walls.
Stuff is still flexible and has not broken down. Used it to seal any holes that were drilled into floor where wiring or water pipes entered the rig, and all still sealed. When dried it was like a thick rubber grommet.
Any Lowes or Home Depot in the caulking area, or roofing area where flashing is sold.

 

[Eddo Rogue]

At the movie studios, we use super77 and super90 spray adhesive for just about everything. I forget which is which for application, but I think you want the 90.

 

[19Walt93]

It's a great time to learn how to weld and being under the bed your early shabby looking welds won't show.

 

[Snoranger]

Pretty much any quality panel bond (stick with a well known brand name like the 3m stuff you posted) should hold up for your application... it’s kind of what it’s designed for.

 

[Jim_Philly]

Thanks all!

Don't get me wrong, the Harbor Freight $99 flux welder is tempting, haha, but I just don't think I'll use it much. I'm more of a hack carpenter, not a hack welder...

Plus, this truck is rust-free otherwise, these two supports are only rusty because of the stupid fabric-like exhaust heat shield they apparently used on the bottom of the bed in 2003. The truck has an otherwise pristine bed floor with a solitary rust hole right above where the muffler pipe jogs up and over the frame crossmember (guess where else I'll be using panel adhesive...) Never thought I'd say the aluminum heat shield that would inevitably get loose and rattle off on other years was a better idea.