I would not remove the tanks. The gray one you could just leave the valve open. The black tank I would suggest leaving the valve closed and opening it as needed, witch will not be that often.
You greatly reduce the value of the trailer if you were ever to want to sell it with the tanks removed. I see no advantage to removing them.
Permanency may trigger a tax liability depending on your location.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles