All above are good suggestions everything is a compromise.
If I were to recommend one overall rig not to big not too small bullet proof climb anything carry any thing get a Dodge/Ram 2500 short bed Cummins diesel. Auto trader has at least 20 with the price range you are thinking of. For pure stealth a white one and add a white aluminum contractor shell and you will look like a government or service truck and when not in the woods you can park safely in any light industrial area.
Keep the lift minimal as well as tires and wheels skinny though.
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Portal build thread:
Okay, this is my first build thread on this forum and I'm happy to finally be starting it. So a little bit about my rig as it stand: Bought it about 9 months ago with 140K miles on it. Truck Specs: 1999 Dodge 2500 5.9L Cummins 47RE Auto 151K miles and climbing 265/75R16 BFG AT's MODS...
www.expeditionportal.com
See this write up:
Finding the perfect rolling home for an off-road, overland and adventure sports enthusiast who wants to travel the globe is no small task,
www.dieselworldmag.com
This rig is now the Down to MOB guy with tons of vids. Probably has 400K on it by now only difference is you keep the stock bed and shell and skip the big camper. You can always upgrade to a bigger camper if you find your plan is space limited in reality. Can't do that on a Taco or Nissan or any SUV like the Seqouia.
This engine will go 250 K if taken care of and another 250K on a rebuild. Truck will go anywhere you can take short of a rock crawler trail and come back. Tons in scrap yards for cheap replacement parts.
For what you stated in your OP all the "Mid-size" are all too small and don't really get better mpg. A good tune on the Cummins and you will see 20 mpg.
I have a 3500 dually and it's a freight train in power and get 17 mpg all day long at 100K miles.
Check this number out Stick and I bet can be had for less than $5k dealer probably paid $1000.
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