I didn't like the E Bay Masonite panels, they were to thin for me.
Mine are twice as thick and have a Formica backing on them that face toward the inside of the door for moisture control. Most old wood panels have some kind of water damage that cause them to warp. I can also bang on them, or lean heavy stuff on them and they don't distort of crack. They were also quit a bit cheaper for me to make. I don't like the idea of a foam backing, seems like it could get snagged on something easier. I've also insulated the whole inside of the wagon so I wasn't concerned about added insulation.
I never consider time when I'm doing something for myself that I enjoy, I just never consider the cost of my labor and put a dollar amount on it. If I think I can do it myself, do a good or better job, and less out of pocket expenses, I think I'm ahead of the game. I probably spent 100 bucks or so on all material, including wood, the adhesive and grey vinyl.
I actually found the rear arm rests in the color I needed, new old stock, on E bay. Then I found the same material, and had them sewn together, then I installed the red material over my existing front arm rests. Now all I have to do is wait several months for my knee to heal so I can drive it again. It's not as satisfying to have my son come over and drive it for me so it doesn't just sit all that time !