>I was told that the Sightseer is not designed for winters.
Neither is any other motorhome! And apart from a few RVs which have un-enclosed holding tanks which are exposed to the elements, rather than being enclosed in a heated basement; most are capable of at least *coping* with winter. Winnebago products tend to be amongst the best designed RVs out there for cold weather camping.
For long-term cold weather RVing, the primary concerns don't really go beyond having to re-fill your propane tank every 3 or 4 days.
Preventing your water hose from freezing is a non-issue. There is no need for a continuous water connection. Simply get the water hose out and refill the fresh water tank as the need arises.
Since Winnie basements are not at all insulated, that's the first weakness I would address. IMO, the simplest and least expensive way to address this issue, would be to pick up a few sheets of ultra-cheap styrofoam insulation from Home Depot; and line the most conveniently accessible uninsulated areas of your basement.
While electrical heaters are economical, and will keep your rig appropriately heated down to about 32F; beyond that, you have to consider how much heat is getting into the basement to prevent freezing. It's a really good idea to have thermometer mounted in the basement for the purpose of monitoring what's going on below.
You might benefit from perusing the website of a vetran Winnebago winter camper: