I have non opd horizontal tanks in my Lance , if I ever have an extra 300.00 I`m going to replace them with new opd`s
I was told the old horz non opd`s can be filled in the camper , don't remember the reason , but new horz opd`s cant
I think it might have had to do with a different filler fitting adapter on the stations hose , that wouldn't work on the newer tanks , new tanks have the valve offset from center , old ones are in the center
Anyway good luck finding a place to fill one in place , most places you have to tell them what the rules (laws) are , their just used to filling up-right opd`s
I wonder if you could get a bolt in place motorhome type tank that would fit from a recycler that might fit
