We talked about theft on another thread a few months back (a member had his 1st gen Tacoma stolen from a parking lot in CA). Unfortunately if a theif wants your truck or what's in it, he is going to get it. The best thing you can do is make it difficult to steal (engine disabler, locking braces on your deck, alarm system, etc...), make it easier to recover (GPS tracking, VIN etching, etc...), or make it less appealing to steal (like you can do that to a Tacoma).
I would go with what you want (double DIN) and just be careful. That is what I do (plus the upgraded security system and the engine disabler ).