Can water heater run while towing? Here's why . . .

If your water tank sets on a platform, as opposed to being suspended by straps, you could slide a coil of copper tubing under it and pipe it to the engine coolant. Winnebago uses a similar strategy with their "Motor-Aid" water heaters that have an extra pipe welded in that has coolant circulated through it (when you arrive at your destination, the tank is pre-heated). I'm assuming water tank plastic can withstand 200 or so degree heat....