at smaller shows bass race will be the ONLY class where everyone has a fair shot at winning. You can't do 20 diff classes with only 20 competitors showing up.
I've done a lot of local shows and they usually do 3 classes: trunk, SUV, modified (wall). Not very fair, but again it's a local show so you should be going to hang out and meet people, hear other cars, etc... Unless you're really into plastic trophies LOL
Make people meter on music, no tones and let them open a window/door so spectators can hear it.