Not on a Thor, but we use ADCO covers, too. First year it looks great. Second year you will have some small holes that need repaired, and maybe a small rip, or two. Third time that you put it on you will have longer tears to fix (some horizontal, some vertical). You will prolly need to reattach a couple of the straps, too.
The maintenance is easy. We drape it over a picnic table and just glue the holes and rips shut. If that is not possible, we sacrifice the storage bag that it comes with, and glue a patch over the hole.
I've never used one more than three seasons. So my cost is less than $100/season, subject to local sales and promotions. If you can get five years out of one, that would be great!!!
Ken, Deb, & Gadget (WIT Club, FMCA, SKP, and grateful volunteers with Habitat for Humanity and SOWERs), traveling in a well-behaved 2005 Winnebago Vectra 40FD w/1100w solar, some gee-golly-whizbang, and a TRAILERED 2015 Cherokee TrailHawk toad.