If you bring ANY motorvehicle from the UK, it's going to have to go back! Plus you're unlikely to get a UK insurance company to cover you past Istanbul. So, you'll have to buy further cover once you get into Turkey.
Travelling down through Europe by car sounds very exciting and romantic. Believe me, it ain't! Been there, done that, ruined the t-shirt in the wash! LOL
My suggestion is to get a flight to Istanbul. See the sights there for a few days. Drop your personal stuff with a carrier for onward shipment to Fethiye. Then, travelling light, you can do a few coach hops down through Turkey.