Since you've successfully drained the tank, you might be able to pressure-test the tank now rather than waiting all winter. It will be a chore, but if you can't bear the thought of wondering all winter, perhaps it will be worth it.
How to do it.
- You do not need to undo all your winterizing. Leave the water heater bypass valves so they are bypassing the water heater.
- Snag your pressure regulator valve from your freshwater supply hose. If you don't have one, now's a good time to buy one.
- Your local hardware store will have an adapter (or a series of adapters) to adapt the pressure regulator garden hose fitting to the 3/4" male pipe thread needed to fit where the anode is.
- Pull the camper out of the garage and partially set it up so you can go inside and open the booth seat to view the hot water heater.
- Hook up the adapted pressure regulator to the garden hose...or your pristine fresh water hose.
- OPEN the hot water heater pressure relief valve to allow air to escape the hot water heater tank as it fills.
- Turn on the water supply.
- When water starts pouring out of the pressure relief valve, close it.
- Allow the system to pressurize while you run inside and check for leaks.
- Have a partner at the hose valve ready to shut off the water if there is a leak.
- If there's no leak after about 10 minutes, you got lucky.
- If there is a leak, first verify where it is, then have your partner open the pressure relieve valve ASAP to relieve pressure. Then remove the hose and pressure regulator and dump the tank as quickly as possible to keep the inside of the camper dry.
- If there is a leak, setup a fan, open the door and a window and ventilate to dry the interior.
This can wait until spring, and you can accomplish the same thing by simply connecting to your home as if you're connecting at a campground. But, if you need help installing a new hot water heater, knowing now will enable you to take advantage of RV repair shops' slower periods to get it fixed.
I hope you got lucky....and I think you did. Slush won't break things, but it is possible that plastic fittings on the tank might have been damaged. If so, you might be able to replace these PEX fittings yourself very easily.
The most challenging items might be the pex-to-tank adapters, and I suspect they are just male-thread-to-barb adapters that can be backed out with a pair of pliers. That's just a guess, but plumbing is usually pretty simple.