I use a cover on an 8318 and had one on my 2601 prior. There is nothing like washing your trailer to put it away, then going back a month later, pulling the cover off and it still being nice and clean.
Plus, if you live in a warmer area or have a lot of sun beating down on it, it really does help keep it cooler.
Yes, they are some work putting on and off, but I think they are worth it.
As far as price goes, $499 sounds way high. I think they (the Adco's) are right around $300 at RVW and other online places.
p.s. Measure the BOX length of your trailer and get the size for that.