Hi, I sikaflexed a load of timber lengths onto the metal floor and then screwed the floor to them. It worked realy well! I also insulated and flash taped in between the timber which made a massive difference to the sound levels (no exhaust noise) and less road noise.
Its has got to be as near permanent as possible or it will shift. Using a polyurethane adhesive is the recommended method.
Brute force will remove it if you ever have to and to avoid holes in the floor you must "glue it down". ( I wish the guys who installed the ply floor and lining in my van had heard of it. Blooming holes every where and they also used wood screws ! )
My original ply floor (Probably like many others? was held down with screws)..
For our conversion though, i have put 9mm batons down ontop of the flashbanded floor, between the ribs & the new floor, will lay on top of these (well foil insulation first) using the 6 lashing points to hold it down.
I got the company to only cut the holes as wide as the lashing bolts so i don't have to worry about getting the cups to sit them in.
I can then remove the floor as & when i require to clean underneath, or even to run cabling for any future elec goodies we might fit in?