A good masonry supply store should have perlite, big bags cheap.
In addition to a well-sealed blockoff plate, if you stuff some rock wool good and tight up around the liner at the bottom it will make a seal that the perlite shouldn't sift through. An easy way to put some redundancy in the system.
I'm not sure on this, but it is possible by using perlite instead of wrap that the liner won't technically be to code, since that application is probably not listed for the liner you're using.
Didn't stop me.
In addition to a well-sealed blockoff plate, if you stuff some rock wool good and tight up around the liner at the bottom it will make a seal that the perlite shouldn't sift through. An easy way to put some redundancy in the system.
I'm not sure on this, but it is possible by using perlite instead of wrap that the liner won't technically be to code, since that application is probably not listed for the liner you're using.
Didn't stop me.