You didn't specify anything about a) towing capacity or b) interior volume other than be able to sleep in it. Sounds like you aren't planning to haul a 5 YPH trommel into no mans land over boulders. So I'm going to disqualify larger vehicles including my favourite - Yukon XL 2500 4x4 with the 8.1 litre engine (and the same interior space as the Carlsbad Caverns) - on point 3 fuel economy alone :)
Lots of good suggestions - I like the all Toyota and Isuzu options mentioned here myself. One point that maybe should also be on your list of criteria is "reliability" - which rules out Jeeps IMO. I'm also disinclined to go off-road with "newer" vehicles suffering a +/-30% annual depreciation (not to mention top to bottom wear and tear on everything from paint to frame , from overgrown bush, rocks, sand, mud, and cargo). That, and the needed on-board factory trained technician Luigi connected via a high speed internet connection to a Cray supercomputer to converse with the electronic toys on board, to determine which one put the vehicle into "limp mode" at the worst possible time, because the filler cap is loose. Not joking. Stuff it if you can't fix it with a 9/16 wrench and get an alternator at the gas station in Outer Podunk. Please trust me, BTDT - helicoptering in a Jeep electronic module can really, really ruin your day.
So, all things considered, in your application I suggest an Audi Allroad Quattro with a Thule roof box on it for your detector, and go wild.
rex