There are fields that now stock mogas but they are few and far between.The oil you would have to take with you.400mls of oil per 20 litres is the normal mix so depending how far you are intending to go you would need to know your fuel burn and therefore work out roughly how much oil you to carry.
Two strokes will burn between 8-18ltrs an hour depending on engine size/pob.
The second generation trykes will potter along quite happily at 55mph and some have a 65ltr tank which gives you quite a good range thus reducing the amount of oil you would need to take.In the past ive poured the oil into the tank in as its been refuelled at the airfield pump which can be hit and miss for acuracy or another way is to draw 20ltrs in to a jerry can then pop your 400mls into it and the stick it into your plane.All part of the adventure of flexwing touring!!