I love the idea of the mat/sit pad idea, and I must say that yours is much more advanced than mine. I just use a peice of wal-mart blue cc foam for my pad. I am definantely making your version tonight!
I know alot of people use the end caps you are talking about. Could you PM me with plans to make them or a place where I can get plans/ buy the end caps. Thanks sorry to hijack. I digress.