The way not to do it is the way I did it. So far I'm still alive and breathing, but tomorrow may be different.
My car was on a rotisserie. I crawled inside when it was upright and disc sanded/wire brushed the bottom. I wore my paint mask while doing this. The sides and top were in good shape. The top had only red/brown primer as a finish coat. Priming was done with spray can rustoleum. It's fairly easy to get to most areas when the car is flipped or rotated on the sides. Just stand on the floor and reach in, or crawl inside the flipped cockpit, crouch on the floor, reach in and do the boot top (inside). It's pretty much obligatory to crawl inside if you want to do the very back of the floor where that seam bends down and the fender wells. These I did first. I have a good mask, did sections at a time, and held my breath when I sprayed.
The paint was another matter. I used the same techniques but used my old Binks siphon gun. The whole inside was done in body color (enamel). Though I tried to spray in short bursts, holding my breath, the overspray and fumes were awful. Lacking any sense whatsoever, I kept at it and finished the job. It was truly awful. If you are using any solvent based paint, you really should have an air supply hood/mask. Be forewarned. Good luck, stay safe.
The AH Spares trunk kit is made with the proper materials (can't remember the name- the heavy leatherette material with jute back). Mine included the piece behind the seats, the fender well fronts, and the rear floor. Also came with grey cardboard pieces for the rear sides and naugahyde material (in my case red) to cover the rear of the fender wells. I couldn't figure any way to glue in the naugahyde on the rear fender wells, so I left those pieces off. The cardboard pieces (probably truckboard) required trimming in order to make them fit. The cut and sewn heavy stuff fit OK, but it takes some figuring to make the fender well fronts glue in around the exposed metal seams.
Jim