Both petrol and diesel suffers from deterioration over time (with diesel it's known as waxing and occurs in cold temperatures), but the solution of leaving the car almost empty and getting it to the fuel station on electric power seems a logical one. There are other ways: leave a small amount in the tank and add a litre or two of fresh fuel every month or so to refresh what's in there, or fill it to the brim with premium fuel as a large amount of high-octane fuel deteriorates less quickly. You can also use a fuel stabiliser liquid.

PHEVs still run a typical 12v car battery alongside the lithium-ion battery, so your C-tec charger should work. As for the main battery powering the electric motor, leave it with at least 80% charge in it.