Selling/Buying: Selling might be a challenge but now is probably the best time in years to do it on the road with sales thru the roof. Plan on stopping somewhere for a month or so because realistically, you will have to show it to potential buyers. Probably in Michigan, so you can transfer your stuff to the new RV or if you have a friend who can show it, put it in storage near them (and make sure they have a good understanding of how things work). It will still likely by a bit of a hassle doing paperwork remotely but certainly doable.
Domicile: Unfortunately, it's not fill out a form and you have a new domicile...you have to build up a case. With "normal" people, it's clear cut because everything is quickly transferred to their new state. Key items are they sell the old house and buy a new house. Likewise, their job moves from the old state to the new. License, registration, utilities, etc...all transfer to the new state. They wind up spending upwards of 90% of their time in their new state. It's all very obvious and clear cut.
As a full time traveler, you don't have several of those key data points, so you need to make sure as much as possible that what you can document that you aren't domiciling in NY.
If you will still be spending significant time in NY, you may have difficulty changing your domicile. They aren't dumb and if it's going to cost them tax/registration dollars, they will challenge it, if it's not clear cut. You want to get your license, registration and other bills assigned to an out of state address...cut as many ties as possible. Get a mail service in your chosen state. Consider starting a blog which documents your travels showing that you are not living in NY. Ideally, also, try to keep your time spent in NY limited. If you spend all summer in NY, they may treat that as you still living in NY.
This isn't to be alarmist. Lots of people do it and it's perfectly legal...just make sure you are methodical and you shouldn't have to worry about it.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV