We will be going through something similar this coming spring. We are selling our house and moving full time in our van. I retired at 47 as a Professional FF. The goal is to allow my wife to retire at the same age and we can just go and do the things we want to do on our own timeframe.
This is what I've learned so far from our financial adviser and tax attorney so take this for what it's worth. You must have a physical address somewhere. Not speaking from an insurance perspective though that certainly needs to be factored in. From things like being able to receive mail (I understand that you can have it sent to a PO box) but... If you get a jury summons you will have to have a proof of address. To pay taxes... The man is going to want his money and there is no way around that. So whatever state your vehicle is licensed out of, you will need a physical address to assess that vehicle. You will also need a physical address to pay state and federal taxes. From an insurance perspective, someone mentioned earlier that where you have your vehicle addressed out of can greatly affect your rate. When applying for insurance they take into account where you "currently" live. If you live in a low crime neighborhood your vehicle insurance will be less. Then remember that insurance companies also take into account how many miles you drive per year etc...
We have a Progressive policy and we have been forward with them about our plans. And quit honestly, the rates are actually not bad considering they are insuring a converted 4WD 2022 Mercedes Benz Sprinter with every single option available. Insurance coverage for $180,000 + $15,000 for items inside the van (think of it as a renters insurance rider) comes out to $89 a month. That is also with uninsured motorist, roadside assistance, etc...
For the time being, we will be using my parents address so we will have a physical address. But we will pay taxes in this state. From federal income tax and state income tax (which I am excluded state income tax because of my retirement pension).
So as much as we would like to completely disappear off the grid? It is impossible.