We had the option of ordering our 186 with a package that includes tank heaters (which they said are just heating pads) and an enclosed underbelly (which they said is a lot like coated cardboard). I think it was $800. We declined. Although we camp all winter, we're in N.C., where the temperatures can get in the teens and twenties but rarely stay there for long. We have camped in the teens and simply unhooked and drained our water hose until morning. Nothing froze that I know of. The dealer told us that frozen tanks are not a problem unless they are full and unless you need to dump them before it warms up. Of course, having access to the fresh water tank would be a different story. We carry a jug of water for the toilet in case the fresh tank is frozen. That package could be the answer to the problem you described.
2013 Surveyor SP220
2010 Silverado LT 5.3 V8
The world is a great book, of which those who never stir from home
read only a page. - St. Augustine