I don't have directly personal experience with this but my Grandparents live most of the time in France and part of the time in the UK, and they have a UK registered motorhome which they are in the process of registering in France specifically because they can't get insurance on it without MOTing it every year, which means bringing it back to the UK once a year just for that. Right now they've let the MOT lapse as they are getting it registered over there, which means they are in limbo - it's not MOTd so no UK insurance, and it's not registered in France yet, so no French insurance. My Gran was complaining about it to me because the weather has been so nice and they can't use it (legally)