I came across an interesting home made approach the other day. A guy was playing an electric 'stick' bass through an amp made by cutting a speaker hole in the side of a small aluminium case, of the sort used for cameras and microphones. He's installed a 10" speaker, and this is driven by a small but very powerful amp from a car stereo system. The whole thing is powered by a small 12v motorcycle battery, and there are input and charging sockets on the outside. He even had a little reverb/effects unit in there too. It sounded great.
Tim