In my opinion THE most important thing to consider when deciding to get a new address while on the road is this: Insurance rates. Insurance rates differ dramatically from state to state and can vary my hundreds or thousands of dollars per year. This is one of your largest FIXED costs when RV'ing.
I know others worry about taxes, and drivers licenses and all of that but the reality is that if you are retired state taxes are probably not going to be a big issue for you unless you have gobs of income.
Yearly vehicle registration is a consideration but is generally not that expensive.
The one time vehicle sales tax should not be an issue if you have paid the tax in another state. Most states will give you credit.
Sales tax is a non issue unless you intend to buy an RV in that state and license it there. Or unless you are going to be resident in that state for long periods of time.
Avoid any state, such as Virginia that has a personal property tax.
I would look for the state that has THE Lowest insurance rates with the lowest overall tax structure. That includes income, vehicle and sales.