Really depends on the how much force and what type of force you expect it to see. If its just a frame that will be experiencing torsional force, 5200 or sika 252 would be plenty. If it will also be experiencing any sort of peel force, I'd recommend a structural epoxy. Is it just a frame, or a frame you plan on attaching stuff to? Keep in mind 5200 and sika take almost a week to cure. 5200 comes in a fast cure variety that takes about a day.
5200 is an incredibly strong bond, but it technically isn't considered a structural adhesive. A toughened epoxy like a proset 176/276 is quite a bit stronger in terms of peel force to remove, yet still flexible. If there is a moment of force, such as a mast or outrigger etc, about the bond site, I'd recommend the proset, if not, 5200. More expensive ~ $50 (although you get about 50% more) and it requires a special $100 two cylinder gun to apply. Proset is also much easier to work with, clean etc. I've used alot of both in my project and I am very careful when applying 5200.
A properly glued project (scuff the surface well, wipe down with acetone, degrease the metal, scuff it well and wipe down with acetone) should be quite a bit stronger than a weld. No disrespect to welding, but if you consider the bond surface at play, a weld has to be many log factors stronger to compete because the adhesive approach has such a greater surface area to work with.