take the floor pieces you cut out and after reading up on some proper welding techniques as far as clean and ready goes start practicing. That thing will spot things in if you just take some time with it. The pipe fitter who welded up my oil pan showed me that. It's not pretty and it's slug slow but learning how to use it will get you way farther than learning how to mix up glue. Speaking of gluing.... how many clamps have you got that will work on that floor panel? Panel adheasive (3M 8101) works great but it's not velcro, and may need more fiddely prep to make sure the surface is ready than welding would. Proper grit no grease or oil (On a truck floor?)
Learn to weld that thing or buy a plastic car I say...
One key I found helps me with welding sheet metal is using a copper 'spoon' as a heat sink on the back of the weld. and it helps to keep from blowing out. the tighter the better.
