Since you are retired, I assume you have investment accounts. I am not going to pretend to be an expert but can relate my experience with my brokerage house and banks.
First, and this my understanding, but do check for yourself, if you keep moving and stay no place for 6 months in 12 months no country can claim you as a resident, but more importantly the US financial institution will not see you as anything other than a US resident and that's the key. I believe this after some long discussions with my brokerage firm.
Second, if you do become a resident of another country or spend 6 months out of 12 in another country, my experience is that you will have a few more things to deal with.
My bank, I think the largest in the US, by policy, does not allow foreign resident account holders. But it's don't ask, don't tell. They accept PMB account addresses, so that's not an issue.
My credit card company, same as my bank, has the same policy, and they wanted a real address, but that can be a friend or relative. Again, don't ask, don't tell.
My brokerage firm, again, is one of the big boys, does not allow foreign resident account holders. But they also accept PMB's. Again, don't ask, don't tell.
Get caught, and you have some hurdles to jump.
So, to avoid the residency trap, keep moving. 90 days in the EU, 90 in the UK, 90 in the non EU countries, return to EU. (No, dont cut it that close) But find a Schengen calculator online and use it cause it's a tad tricky cause 90 in 180 is a sliding scale. I played the Schengen game for a few years and finally just picked my favorite county and got residency. It is so much easier to do life on my, not Schengen's schedule.
I use my US ATM and US credit card daily in the same European country.. Some day, some computers will put 2 and 2 together, and I may have an issue, but so far, so good.
My PMB sends me a scan of the outside of every piece of mail I receive. Then, if I ask, for about $1, they will scan and send the contents. And they will forward mail for a small fee. Very convenient. The storage room in Texas, larger than FrankII's, is cheap.
My European medical policy isn't real cheap, but it pays well and covers everything with a high limit. Then I have an expat evacuation policy with MedJet and I maintain my Medicare Advantage policy.
All of the extra costs are substantially less than the cost of owning a car in the US. And being here I can go to the airport and get on a $30 direct 1.5 hour flight to anyone of three dozen destinations. Europe and parts of Asia are cheap and convenient to reach.
My flat costs less to own per year than 30 nights in a hotel, so that works better for me.
But I ramped up to this slowly over 20 years, and seriously for close to 10 years.