Restorium,
Some large class A coach RVs have heated basements so the water heater is less sensitive to cold weather while occupied over the colder months. But any UNATTENDED unit should have its water system winterized, either by adding RV antifreeze or by completely emptying the plumbing system using compressed air.
I lived full time in my 2007 Tour Master for more than 5 years so did not need to drain my water heater during that period. But there are many on-line check lists like the link below that clearly state to drain the WH and then bypass it before you add the antifreeze...
http://rvservices.koa.com/rvinformat...-checklist.asp
Chuck