I added a set of frostless faucets to the outside one Ted off before and one Ted off after a ball valve in my cold in to the heater. attach tank to those with top to the after faucet and the first faucet to the bottom [or dip tube] of the tank. That way, come freezing weather you just turn off the faucets, remove the lines, open the ball valve and you are back to "normal". When using the preheater you close the ball valve to force water to go through the preheater. My water heater is within a few inches of the north wall of the house and I bought good quality washing machine hose to go from the faucets to the tank.

You could easily do it both in and outside with some thought.

Good luck with it.

Tom