Rusty floor pan!

I've never liked the idea of panel adhesive on a unibody car floor. As said, the floor is very much a part of the car's structure. IMO, over time, flexing will work loose the adhesive. Think of all the trouble you're going to go through measuring, cutting to get everything just right to fit. You're only going to want to do all that once. Welding will be permanent. Get everything measured cut and ready and go rent one.