With propane prices headed for the stratosphere, I am looking for ways to better insulate my 16x20 greenhouse glazed with 8 mm twinwall polycarbonate. The north wall and north roof slope have rigid foam and foil insulation, vents and door are insulated. East and west walls have poly sheeting stapled to the inside of the wooden studs everywhere except above the heater. That leaves the expanse of south-facing roof (it's an asymmetric design with long south slope and short north slope). Bubble wrap inside is impractical due to cross braces and purlins, not to mention the requirement to shift benches and hanging plants to fit a ladder in.

I have been reading the archives from a few years back when there was lots of discussion about using Magni Clear pool covers as winter insulation. Can anyone report on results over several seasons? At least one person suggested that chlorine outgassing from the vinyl (?) would degrade the UV protective coating on polycarbonate. Has this happened? I'm intrigued by the possibility of using a cover, but I don't want to create bigger problems later.