Here's my only input on this, which is likely not to be the opinion of many but that's of course OK. I went w/ a cheapy...my only criterai is that it is water resistant. The reason for this is b/c in my exp (which has been years of using a cover) these things often develop some mold on the inside. Not much, but enough to where you want to replace it every few years. In addition, I wanted something that really looked generic- I don't want a big red Husky cover w/ the logo advertising what's underneath...better to be inconspicious (depending on where it's sitting.) Now if you park and need to cover right way then you'll have to focus on something that's truly heat resistant in the right places- up high and at the rear in the 630's case, esp if you have the stock cans.
