I am sorry rayc but I am fairly sure your suggestion of the European option is not valid.
We used to have a 4.5t Hymer and we both both needed to renew our C1 licences. It’s a pain but unfortunately necessary. You can download packs D2 and D4 - I think those are the forms check it out. Things change. You can also apply on line for them to send the pack - that is best option because the medical form is pages long. As previously said you can apply for your medical four months previously but that won’t help if you are away for longer than six months. We have known people who flew home from Spain just to do their licence. When you do submit your application you have to include your licence. It can take up to three months to get your licence back. My husband was recalled for an eye test (he has no medical problems with his eyes they just wanted a field vision test - even though he had had one two weeks before he submitted his application) so that delayed his for about a month. I do have minor medical issues which required medical reports from the hospital which I arranged in good time. Mine took three months. I rang the DVLA medical section a couple of times but they just fend you off with ‘pressure of work’ ‘it’s on someone elses’s desk’ etc. One year we even went to Swansea (from Scotland!) en route to Spain - to hand it in. I didn’t include my licence because I had misplaced it. We intended to wait a week but they said anything with a medical report takes longer. So we went off to Spain and my daughter eventually posted out my licence to me. In the meantime I rediscovered my misplaced licence so I was OK for any ad hoc road checks. However, it’s not all doom and gloom. Some folk get their renewed licence with a few weeks.
I am afraid my only offered solutions would be to fly home for a couple of days for your medical and separate eye test or adjust your trip dates to suit. Not an ideal scenario if you plan on wintering in Europe. FYI my doctor needed good notice for an appointment for private medical (£100) the optician only needed a few days.
Good luck.