I just had one of those "D'oh" moments.
My "Use Dunstaffnage" theory was because of the atrocious fuel consumption of the car over the hills to Easdale. You are the "right side" of those hills, and I hadn't realised how far down the sound you are... (Thus almost allowing me to do the whole trip on what I can carrry. D'staf would mean borrowing yet another tank.....
Whats your launch / recover / park fee? (It's the one thing I can't find on your price list!) And are the showers open "after hours"? (I'll be recovering sometime on Saturday evening after the food).