I’m Happy with my Racewear (brand) Kart Cover.  A fair amount of EKN supporting shops carry them.  These have kept my karts clean and dry.  The elastic bottom fits well and we’ve not had any problems with them coming off in typical environments.

We sell 3 different brands from $45 to $55. The biggest difference is appearance. http://www.accelerationkarting.com/kartaccessories.aspx

I agree with Jeff. Raceware is literally the only cover I’ve put on a kart that actually fits without precise positioning or yanking with all your might. That plus quality materials and assembly kept it in use for a long time… two karts ago to be exact.

get some tarps from harbor freight.

They’re bigger, and definitely not as “pretty” or form-fitting (which can be a benefit because you don’t have to align things perfectly, etc), but you can find small atv covers (the bigger ones are “too” loose) at places like Walmart for a lot less money than kart covers.

They have enough elastic that they won’t fall off (shove some of the “excess” under the tires for better cover, and less slop/bulkiness), and unlike a tarp (which I’ve used before and is a pain), you don’t have to devise other ways to secure things so it doesn’t fall off.

http://www.blackdogvintageracing.com

we make custom kart covers .