That would be my suggestion. You say "a little more nose down", does that mean when empty your trailer is nose down? I would see if I could get it level.
Lets go with the 40 gallon tank. Full it would weight 320 pounds but you say you usually travel with it half full. So, the difference you are adding is 160 pounds. Unless these 160 lbs are sitting directly on the tongue, they shouldn't make that much of a difference.
I say adjust the hitch. If you can't do that then move some of your existing weight to behind the axle.
2017 Toyota Tundra, Double Cab, 5.7L V8
2006 Airstream 25 FB SE
Equalizer Hitch