You can't fill a SORN out anymore when taking the car abroad if you don't want to pay the road tax.You would have to export it and then re-import it when you bring it back which is very expensive. Also my insurance company assures me that my insurance is invalid if the car is not taxed and MOTed. This has all come into play since the recent new goverment car tax computer was introduced.
It is also now not possible to insure your car in Greece.
Another thing to watch out for is that most companies now only insure you for up to 4 weeks abroad and you have to pay extra after that. The only company I found that gives unlimited time abroad is Saga and you have to be 50+ to insure with them.