If you truly do want a TT for winter use, an enclosed underbelly will not be the only item to look for... look for the heated underbelly or tanks with tank heaters on them. Last thing I would want to deal with is a very sudden temp drop and problems with freezing holding tanks... that would be nasty. It would also not be great to have your fresh tank freeze or any of the tanks with valve damage because of freezing.
An item to be aware of, true 4 season TTs are usually built with better quality methods and materials which equates to higher pricing. Have you noticed how much higher priced Arctic Fox TTs are?
