Most 4x4 pickups with a transfer case that can be put into neutral are towable four-down. For example on my Silverado you could put the transfer case into neutral by following the instructions in the owners manual. After the transfer case is in neutral the vehicle can be towed with the gearshift in Park. Seems weird at first, but the transmission isn't turning since the transfer case is free-wheeling.
You can check
Remco towing for detailed information about vehicles you are interested in.