The right way to line a tub
I lined my tub last year. To do it right, take out the entire interior including seats, gas tank, steering column, heater, rollbar, tranny hump, kick vents, rear side marker lights, everything. Disconnect and hang all wires/cables. I used a combination of several types of sanders bought at Home depot. I used a random orbital, a mouse, and a particle impregnated round brush on a drill. Wear goggles. Sand the whole tub. The hardest part is the corners under the kick vents, esp. on drivers side. You may have to hand sand some. Prep all the way up the firewall (if you want that lined; I did). I used 80 and 60 grit. The liner sticks better if the surface is rough.
I wanted to line up and over the rales and over the door sill. Therefore I taped off lines about 1 cm "over the rails" (see pics). I then hand sanded above the tape. I also lined about 2 inches below the door sill for a lined "kick panel" area. I found that the blue (3M?) painters masking tape stuck best, is durable, and will not damage paint when removed. The brown stuff is too thin. I spent lots of time taping and sanding. I taped curves with many sequential small pieces of tape. I then made little plugs out of blue tape and put them in all the (one million) holes in the tub to keep them from being covered. A year later, I still have bad dreams about blue tape. You can also use Q tips.
I then come-alonged the 40 up on a trailer and hauled it to the liner dealer. I chose Arma Coat. It is sprayed on hot and at high pressure. They have to mask off your whole truck, including the dash, to spray this fine spray. Due to high heat application, it goes on with a finer grain than some. I think it looks more like a factory coating.
Then trailer the rig home and spent the next 8 months replacing your interior because you did not label parts. I also had all metal parts powder coated at this time, but that's another thread. I went to great pain to prep the rig right. I stressed to the dealer that I wanted nothing short of a perfect application since I prepped the tub myself. There is no way any dealer would spend the time to prep the tub like I did. Do the prep work yourself and cut a deal with the dealer.
I cannot comment on the long term durability of the Arma Coat yet; the 40 project is still unfinished (to be done by spring ... 2008). I can say that it took 100 times longer than I thought to do it right. I am very pleased with the factory appearing results.
Or you could just pull the carpet and slap some Durabak on the exposed areas, then drink a few beers. Hmmmmmm...... Opportunity Cost.