To do the paint roller tray floor drop 1-1/2" to 1-3/4" is enough and still give you clearance for speed bumps. Any metal shop can bend and tack weld the floor trays to your specs, just be sure you allow for the material the bends take up. If welding is not your thing or not available you can use adhesive that Mfg's use. I found that 3M Panel Bond. is easy to use and id for metal to metal as well as metal to fiberglass. I built a Smyth Ute VW pick up truck with it.
The duel cartridge fits into a special $65 gun but it is not needed for a one time project. You can cut the two section cartridge open mixing equal parts of the adhesive. There are different product numbers that dictate the dry times, you'll want at least a 30 minute set time. Once the product has cured it is as strong as the metal is is bonded to.