Re: cleaning and preserving boat top?
Can't you fold the top down and use a boat cover? The covers are a lot cheaper than replacing a full enclosure. When you say "full cover" are you talking about an enclosure with top and sides? If so, there are plenty of products you can treat it with, take your pick they all do the same thing. They just slow down the outgassing of the petroleum bases that keep them pliable. You're supposed to fold them up and use a full boat cover when parked in your driveway on a trailer. Enclosures cost $ thousands, covers cost $ hundreds.
I expect that I would pay at least a grand to replicate my original enclosure. I am lucky to have the original OEM enclosure to make a pattern out of - and it is still in decent enough shape to use. I suspect there aren't but a very few surviving examples existing after 47 years.