i bought the Dowco (Guardian) and very happy with it, but it is a tight fit.
http://www.dowco-inc.com/Seg_Power.asp?seg=2
i got the weatherall plus 76.99 you can the two tone the lighter one on the bottom is heat resistant so it wont melt easily when if your pipes are still hot.
also the have one that comes with a built in alarm if someone tries to take the cover off. $119
i read that these covers may be better than just a plain sheet cover as they better resist mildew.. not sure if that accurate.
they also sell some light weight covers for about $35
thanks, good luck