http://www.allencampermfg.com/index.html
We have been doing some remodel work on our 5th wheel and get most of our supplies at Allen Camper Manufacturing in Allen, OK. I realize it's about 10 hrs. from you, but it might be worth a drive up there one weekend to get some from them. We bought ours for $25/sheet. It's the same thing they put in their new Idle Time campers they make.
Lowe's also has some stuff to choose from, but it's a LOT heavier weight. We bought theirs, then found out Allen would sell us theirs. Took the heavy Lowe's stuff back.
Hope this helps! =)