Hot Tub Covers (and Costco)

We have a hot tub cover that is waterlogged, not only that but since we got it it's been getting a nasty looking line around the edges (underneath, water side) that I've scrubbed and cleaned, however this year it looks like there is maybe mold too. So I want to get an new one (unless anyone knows how I can clean this thing some other way). It definitely did not hold up like the original did, which was water tight and sparkly in the underside lining until the end when it was cracked by a collapsed gazebo.

Obviosuly not going to use the same company this time, so thinking about trying Costco but the reviews are older - has anyone got a cover from the recently and how is it holding up? any tips for ordering for sizing etc?

Thanks!

p.s. the water and lines are perfect - the issues are strictly crappy cover quality related.