The 3M panel adhesive will work fine for you - it is preferred by many professionals because welding the panels warps them. The 3M stuff is very strong, it's a type of epoxy. The only problem with the 3M adhesive is you need a special gun to apply it that mixes the 2 parts as it applies and it's kinda spendy.

As an alternative, you should just make a road trip to Central Texas and buy your truck here. Use Craigslist to find one - they are plentiful and rust-free.