Good!
I am Swedish. My uncle lives in Nice. I'll check with what he knows.
I have tried leaving cars at the airport and let me tell you I'm giving it up. I've got a car at the shipyard which maintains my gaff ketch in Göteborg, another car at Åre AirPort when snowmobiling, I have a standby hunting 4x4 Navara in Spain and believe me, it doesn't work. It's a wonderful and extravagant idea in theory but it's a prison. The last two trips to Sweden I picked up a rental and it works like a Swiss clockwork AND it is much cheaper. I only needed a little Skoda Yeti 4x4 with a hitch to pull the trailer for the hunting recovery quad on the one trip and the snowmobile trailer on the other. With a standby car you need to organise maintenance and inspections from a distance and if that doesn't work out you need to do it yourself on your precious vacation. Then you have, tax, insurance, not to speak of DEPRECIATION! Guess what, I'm selling those vehicles. They are in fact a burden.
It's just my personal experience and I don't want to kill your idea but chances are you will fool yourself. Narrowing in your search to an English speaking mechanic, in FRANCE, for a unique car like the G is optimistic to say the least. Let alone the rig being a G300 which surely will need its TLC. Maintaining my Navara and G400 in Spain works because I'm fluent in Spanish and 100% connected in the country but it is still a nuisance dealing with it. My humble advice is to rent a 4x4 when you're off-roading around Nice. Then you rent a cheaper car for all the other days when you're not off-roading. Sell the G in question (assuming it's your second G) and every now and then you drive down with your number one G).
Just my two cents...