Covers are a grill manufacturer's frustration.... It is an item that they do not make, so maintaining quality control is more difficult. And - 1 cover will survive one region's weather - but the same cover will not do as well in another area of the country - or planet....
And - I doubt this is an is an issue in your case, but I have seen some folks put the cover on a pit - as soon as it would not burn them to do so. Be sure the PBC is completely cooled down before installing the cover. The concern here- is not about fire ( tho one can't ignore those potentials either
) but, that the additional heat can shorten the life of the cover because it speeds the aging process. Heat and UV play havoc on all plastics. The more "plasticizers" ( chemical compounds that make plastics flexible ) in a product - the the more they can be affected by heat/UV.
High-quality covers can be expensive. Especially if the cover is for a grill that is not a very common size and style.