the mountains don't use lexan what your looking for is ultra high molecular weight ploy ethalyne (sp?) or UHMW PE. Its high impact resistance and low coefficient of friction make it ideal for boxes. Its what the mountains use. I ordered it from www.modernplastics.com
and it was about $150 for 24 feet at .25" thick with shipping.
"a good anything is good" -j mouans
THINK. FEEL. DRIVE.