Just put my 18' x 52" Ultra Frame yesterday (it's about 1/3 full so far) and followed mccoonan's instructions...leveled with 2x10 w/6 ft level taped to it, used this (http://www.homedepot.com/Building-Mater ... reId=10051) 3/4" rigid foam for the entire bottom, then covered with a heavy duty...