Since we're on the subject of boat smells, Peggie Hall recommended a product to me called PureAyre. I haven't tried it yet but Peggie pretty much raved about it. They claim it will eliminate diesel odor as well as just about every other odor source on a boat. I ordered some for my store but I haven't gotten it yet. When it arrives, I'll grab a bottle and let you know how it does on cat boxes!
PureAyre Odor Eliminator - Marine