OK. For the good of all, I 'fess up.
Over the past 23 years I have been trundling about through FR and ES in my ‘camper van’ [rather too often it being in removals van mode] Yes, even the kitchen sink

A RHD GB plated Vauxhall Movano.
A good deal of the time I continued to be legitimately a UK reg person with a legitimately UK reg van
But from time to time I did stay the 90+ days in ES that would oblige me to apply for residency, with all that implies re vehicles. The ‘snowbirds’ in their plastic cottages on wheels used to spend way over 90 days on the costas and Algarve. Brexit has done for them.
But like hundreds of other Brits in ES I never bothered with residency. UK was still in the EU, the Spanish were very lax on this subject and the daft thing that would have arisen would have been that I’d have to re-reg as a UK citizen when I got back after every 90+ day jaunt.
The rules don’t accommodate nomads.
Then I moved to ES full time. I tried to reg to ES plates. I contacted a couple of guys doing the @anon90504988 thing. For RHD commercial vehicle it was VERY DIFFICULT. Waiting lists for 'CT’s ’ were 2-3 months for locals! - and then it became impossible for Vehicle Category N1.
But I was happy to return to UK to get an MoT when necc . Heading back to UK for another MoT …
It lived out of sight in an enclosed garage in the centre of old VLC - f.o.c. !
Hostal Rincon sadly closed in the time of the pox and was sold. I expect a snazzy block of flats will appear.
Here is el patron, Jorge, minding the shop after his usual bibulous lunch. He was so out of it after one lunch that two women who came to wish him Feliz Navidad could get no reaction despite leaning over the desk and shouting in his ear!

When my flat was being refurbed I went on trips to the bricos for stuff. The route passed by the main barracks of the Guardia Civil !
But I was, as far as all the paperwork went, still a UK citizen with a UK-legal vehicle. Then I got residency and it wasn’t.
But with a current MoT and UK tax and insurance, and me with a UK p/port, we would have passed a check by the G.C. or FR gendarmes.
I came and went on this basis for 5 years.
Then, after getting myself and my car settled in FR, my flat in VLC sold and I set out from UK to do another removals run in the van.
The MoT had run out and so had the tax. I did have insurance.
I had an MoT test booked for the day of my sailing to FR. For reasons to do with my eyesight and driving in the dark, I cancelled the MoT although I had time to do it and get to Newhaven for the midnight sailing. But I was scared of driving in the dark and thought I would wing it. I’d had no bother before - a UK camper van trundling thru’ FR/ES …
All went well on the trip down. On the way back I pulled in to one of those truckers’ cafes way out on the mesa, in the middle of Spain. A Guardia Civil vehicle parked up and the guys went in for a coffee. I was in the van about to leave and did so.
A few minutes later the G.C. guys waved me over into another truck stop.
All was well with my papers except - no MoT, no tax. They showed me the check they had dialled up from DVLA’s ‘check a vehicle’ pages. I explained to them that I had reported the vehicle ‘permanently exported’ to DVLA and had started the process to register it in FR but as far as they were concerned it was a GB reg vehicle without the documents making it legal in the country of registration.
I had a choice. Go no futher in the van [and presumably arrange for me and it to be transported] or pay €350 … €100 for no MoT and €250 no tax.
At €350 it was a deal. I got printed receipts and the cop told me that these would serve if I was pulled over again in ES. [Can’t be done twice for the same offence.] And that I should get a C.T. and C.G. chop-chop when I got to FR.
I don’t think I would have passed if taken to a weighbridge. The tops of the rear tyres were invisible behind the tops of the wheel arches but G.C. didn’t bother with that issue.
The trip thru FR to Normandy went off with no further incidents. I parked up on the farm, booked an MoT for the day of arrival in UK and headed north.
I think that, in the case of more than simply not having legit docs - in an accident, say - the Spanish would impound the vehicle, as I imagine the FR would. The fines would be of a different order to €350 …