I’ve only got rear speakers and they’re in my tailgate. It’s fine with the bed down, or if I haven’t got much in. However, if I’ve got the bed up and have stored duvet etc behind the seat it can cover the speakers a bit.
Front. Kick panels for me. Rear. I've got 4 of them under the full width rear seat/bed. Still hear it easily when in bed. They take up a bit of storage space, but not much. Mine are 6x9s. Other people fit rear ones in the top corners of the head banger locker. Depends what layout you have.
Two 5" in the front kick panels. Two 5" in the headbanger locker. Two subwoofers (actually just 5" full range speakers doing bass duty) under the rear seat Stereo rated at 4x22W with additional 2x100W amp under rear seat for bass. The amp was lying around from another failed car audio project. My wife was amazed at how good the sound was when the engine isnt running. When it is , I have to sometimes turn the stereo down to hear the engine properly (also have slightly upgraded engine bay soundproofing)
Another vote for front kick panels and under the rear seat/ rock n roll bed. Nothing fancy in the way of extra amps, just a normal retrosound unit in the dash. Get the balance right between front and rear, and it’s fine when driving. (and obviously fine when camping) I’ve got lights and USB charging points on the headbanger locker, plus the monitor for the solar panels, or else i think that would be an excellent place for the rear speakers.