Underbody paint advice needed

1) read the directions on what the supplies you have require.
2) truck bed line on your floors? Sorry your car not mine but that is going to be a pain to clean dirt and hold moisture between the metal and the liner. Allowing rot to spread easy. I did that on a cab of a 72’ W200. Sand blasted spotless and allowed the Rhino lining process to do their thing. Professionals. With in 3 years the floors rotted out. Everything perfect to the t. I know off road guys swear by it and my truck was used every day.
3) I wish you luck with this process. I hope your car turns out better than my old power wagon did.