Since it was bought in March, in a temperate zone possibly without great chances of springtime long term freezes , I don't doubt that the op was told what they were told upon delivery.
I highly doubt, with great prejudice, that they were told to not winterize the vehicle at the beginning of every frost season. We're in that next frost season after their purchase.
And those saying to fall back onto the dealer as faulted...
Google how selective interpretation and ignorance of circumstance works.
Dealer has sold hundreds, the op has been slightly involved in one....
While having the heater fixed, op should pay an extra hour labor for an in-depth rv review now that the op has some experience to Help retain info.
Uneducated was the correct word for the situation. An hour of in-person review and this forum Will fix that fast based on op's very pleasant and thorough writing skill.
Wisconsin and no winterizing of every darn thing you own?
Call a residential flood clean-up company and get fans and heaters and an insurance claim started(if insurance will cover)
There was another thread where OP had bought a heated water hose and was hell bent on using it to a trip to Indiana with known zero degree temperatures in the forecast. It was as if he used the forum to get comfort that his idea was valid. He never came back, but it is a good assumption that he used selective interpretation from a few of the post to validate his plight. Assuming he tried the new heated hose, I wonder if he suffered a similar fate.
I agree with assumptions about what this OP may have been told in March. It is akin to when we 1st bought our pool, the pool company said we didn't have to worry about winterizing. Skipped the instructions on how to winterize, but he knew our controller would always force the pumps on to circulate water with freezing temperatures. But he didn't factor in what happens when you had both freezing temperatures and loss of power for week
