I, too would suspect a water line to burst before the tank would. That is, unless the tank was compromised earlier. Two 1500 heaters seem like overkill to me anyway. Best thing is assess the damage and then decide what to do. If it is, in fact, the fresh water tank, call your insurance agent.
On a side note, unless you're boondocking, and it doesn't sound like you are, why do you have water in the fresh water tank anyway? I'd drain that knowing it's going to get that cold. I'm sure the water lines in the park are heated....best of luck. I hope it turns out to be a simple break in the water line. Shark Bite fittings at Home Depot are the best.....Dennis