I get the Mogas to the airfield by driving to my local petrol station, filing 3 X 20L metal cans (or less) and then driving to the airfield! I use an anti static siphoning system to fuel the aircraft.
I count any mix of Avgas greater than 25% as Avgas and count the hours as double. I did not come up with this myself; it is common practice in my local area and appears to follow the rules.
I am off to France for a week starting next Saturday and will need to bring my 50 hour check forward by about 17 hours when I get back, which is a pain. Avgas at my local airfield is £1.40 so lots of good reasons to use Mogas whenever possible.
Rod1