I am also in the SELL camp but with two caveats
1 Michelle needs to agree.
2 You might wait a while for your rear lounge (fixation I will call it)
On point one about Michelle thinking it is worth more, my comment to her would be that when a prospective buyer reads the recent MOT report he/she might be sceptical about how well the repairs have been done and why you are putting it on the market so soon afterwards, and therefore be making some tough negotiations at least down to and maybe below £10K. You have got a 'willing buyer' in your hands. How long before you find a buyer at the price she thinks it is worth - which is what? If she vetoes this chance to sell you need to get her agreement to pay any difference in price below £10K
On point two, it depends how long you are prepared to wait for what your long-term MH, with rear lounge, would take to find. Would you consider an alternative of looking for a good older MH with rear bed and garage as an interim with the idea that you could sell it after finding your ideal, or even 'god-forbid' actually liking it
It would need to be a private buy and resell, to make sure you only lost £1-2K, if not make a profit.
An interim MH would let you get away while you are looking for something else.
An interim vehicle with a garage would make it easier to carry your new scooter(?) without fitting a rear rack and having to worry about rear-axle weights.
How long has the guy given you to decide?
Good luck with whatever you decide.
Mate, you know my phone number if you think I should take my comments and '......off'