I'm in the planning stages, but how does this sound? - A MDF box containing an el-cheapo car radio HU with 4 generic brand speakers (two per side). The radio will sit facing up to the top with a removable locking cover. The speakers will be nut & bolt mounted to deter theft. The unit can be affixed to the floor by wing nuts from the inside to deter theft (remember, the removable top locks!). And to top it off - Rhino Line the whole shebang!