I say go all out and build it for two, and make the walls insulated with a propane heater. Put a funnel and hose hook up in the corner for RELIEF, just make sure to bury the other end of the hose in crushed rock and cover it with sod (no smell). Bring out the meals in a bag and stay all day. I've even seen some guys go to the department store and get wireless drive-way alarm systems which you can set up with multiple sending units and set up a perimeter. All you need to power the senders are batteries and the main unit can be powered by a portable power box. The main unit has up to four zones (sender) that light up and or beep indicating which one was tripped.

What the heck, you only live once.