I buy the 3 mil 55 gallon ones.
They are called barrel liners.
They don't look as sexy as the nice white commercial ones. But until I find a better cover set that works in the cold; these will continue to work for me.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW