pairodice that sounds like a boat plowing water under a serious load getting that kind of fuel economy. What year and what engine are you running? Once upon a time I owned a Foretravel and don't remember getting that bad.
I agree the terrain and personal driving habits has the most to do with fuel economy. The way I see it is how common sense spells it out - If you are floored going up a mountain you're going to get the low side. If you travel at the speed limit on a flat highway you'll most likely get your maximum fuel economy.