Looking at buying a portable black tank - suggestions?

HOw long are you actually staying. A 50 gallon black tank can last 2 people quite a long time.
For the record I have a 42 gallon Barker that works great. I use it for grey water. While if necessary I would use it for black I have never stayed long enough to need it for black water.
The newer 42 gallon Barker tanks come OEM with rubber wheels.