"Gregory Young" writes:

Permalon is the way to go, but when I priced it, it was more than EPDM.
Permalon is HDPE, and is one of the strongest, lightest liner materials
available for use today. Also has great UV resistance. It has a 20 yr plus
guarantee as well.

Can you use the pipe boot trick with Permalon -- is it stretchy enough?

Are you sure about the guarantee, I thought it was 1 year. Not that I think
either will wear out.