For the first time in two years I left the cover off of MR. Egg and during the last 3 days we have had in excess of 2.5 inches of rain. Went out this morning (the sun is trying to come out)to clean him out and I was amazed at how wet the ash and small pieces of left over lump were! I wasn't going to cook until Sunday and may have just saved myself a lot of grief. Cleaned him out and I'm letting him 'air-dry' for the moment.
My dealer had suggested a cover when I purchased Mr. Egg and I trusted his recomedation. I've NEVER had a problem starting a fire or getting the temps I desired. Now, I have to think the cover does its job.
IMHO a cover is a GREAT investment and you can be sure I will not be leaving MR. Egg uncovered in the future. I recomend you get a cover if you don't have one and enjoy yourself even more!