no experience with crawlers, if you want to cover bridge and almost neck-like tones with a single humbucker i'd say holy diver, BUT in a basswood RG you'd have no highs to speak of... nailbomb is very versatile, cleans and splits well (with a very straty sound)...
if you don't want crystal clear cleans have you ever thought about an alnico warpig? i'd get that one if i had just a bridge slot to fill... and it's simply devastating for heavy rock and metal riffing! :twisted: