I would say if thats your future plan save the hassle and don't put it there, put a double box a few feet short of where you plan it will sit on each side (go measure one the size your planning on to see) and make due with a short cord if needed. I wouldn't want one there if I thought it would mean I can't get the most room possible in the room (lost real estate).
I doubt the code would be an issue unless the tank is considered permanent, akin to a refrigerator outlet behind the refrigerator or behind washer and dryers/ovens etc. the unused 220 outlet behind my gas stove would be a code violation in the same manner if this was the case.