Your door is probably the bubbled texture FRP panel. You can get a sheet of it in white at Home Depot/Lowes usually, since many car washes use it to cover walls, public showers use it, etc.
Chances are you will need to rebuild the wood door frame as well due to rot, because that's usually what causes the skin to come off. Otherwise with good wood, it's sandwiched in there tight and doesn't go anywhere.
Still, a very doable DIY project for relatively little cost.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR