Does anyone know of a panel adhesive for metal that can be mixed like regular body filler or epoxy and not require a gun? I'm reinstalling the rear parcel tray in my 70 GTO and Id rather bond, than weld the side pieces that mate to the sail panels. The mating surface on each panel is about 1/2" by about 14" The remainder of the parcel tray will welded.
Your thoughts are appreciated.

3M. They have a huge range of adhesives. 1K, 2K on tubes of various sizes, some that don't need a gun for application.

https://multimedia.3m.com/mws/media/490864O/3m-scotch-weld-structural-adhesives-selection-guide-digital-brochure.pdf

I've seen guys use a single caulk gun with sockets for spacers
on those "duel cartridge" ones to do one side at a time
then mix like you do for fillers.

I'll check with 3M and if all else fails I'll try the socket trick. Great advice guys, Thanks!

I like Panel adhesives when their used properly.

I have a couple of different ones I use, While I do have the special guns that are required for the ones I use, I do skip the special mixing tips and just pump it out on a Paper plate and mix by hand and use a putty knife to spread it on the panel sections where its needed.

And what was said their are some that require plain ordinary full size caulking guns.

I have used 3M, Matrix, Lord fuser, and another brand I can not think of the name off the top of my head at this time. The requirement of needing special guns and special mixing tips is a determinant to some of these products. In 3M's case its just pure Greed trying to make every dime possible off the end user (Just my opinion) .