However, 3 hours flying is 21 gallons per side i.e. 42 USG total. Can be 18 a side if I am careful or even less with a tailwind.
You must have some heavy friends.
Light friends, heavy aeroplane.
With 4 x 180 lb people and 70 lb baggage (excluding the emergency equipment) I get 38 USG in. My rule of thumb is 14 USG/hr (which includes a contingency) + 4 USG excess for t/o and climb. So that's 1.75 hours to destination and alternate + 0.75 hr FRF.