Door panel backers

Evening folks,
Time for me to get started with the interior. I will be doing some type of custom door panel and seats. The backer panels I removed from the car have seen better days. Water damage, edges flaking off, you get the picture.
I was at Lowes yesterday to look into some type of panel material to use. 1/8" tempered hardboard was probably what was used originally, a sheet of that goes for $7. They also carry a 1/8" "tileboard" which looks pretty much like hardboard but is more water resistant - that costs $12-16 a sheet. They did not have 1/8" plexiglass, although it could be ordered for $$$.
Anyone use the tileboard? Any downside? Anyone use this stuff to make the rear package shelf?
Thanks,
C