Look around a few job sites in your area for the green pvc tubing that is
used for water/sewage. There are usually plenty of pieces of various
diameters laying in the trash pile. I have some in 8, 12, and 15 inch
diameters. The bigger the diameter the thicker the walls. I use 1 inch
mdf for end caps. Have used it in trunks and in boats. The big stuff is
heavy though, i have a 4 foot piece of the 15 inch stuff and it weighs about
75 lbs. This stuff cuts easy enough and is easy to cover with carpet.
Jack in Dallas