The maximum wattage on a guitar amp is a little more important than that of a bass amp. Guitarists like power tube distortion, and ass such need to run their amp at near maximum volume to get "tone" out of them. Many bassists either want no distortion, or use a pedal to get their sound.
That said, a head an 4X10 may still be a bit too aggressive for the situation, but a 50 watt combo with a single twelve-inch speaker would probably work quite well. And if you can beg/borrow/steal an Ampeg portaflex with a single twelve-inch speaker, you'll be in heaven.