Hi metal52,
Congratulations on your new-to-you North Trail and welcome to the Heartland Owners Forum.
All of the current North Trail units have 36 or 37 gallon tanks. The
NADA Specs page on the FX23 shows the 2012 also has 36/37 gallon tanks.
Holding Tanks
Fresh Water Capacity (gal / L): 36 / 136.3
Gray Water Capacity (gal / L): 37 / 140.1
Black Water Capacity (gal / L): 37 / 140.1
Propane Capacity (gal / lbs): 9.4 / 40
Water Heater Tank (gal / L): 6 / 22.7
I've moved the thread out of the North Country area and into the North Trail area.