[PSIG]

I'm not convinced that the fuel consumption will be that great, not once you've more than doubled the vehicle weight. Its going to be hard on the clutch too.

Agreed, and this is part of planning. I had this issue with a 1.3L and lots of highway driving. Crappy economy, as it was always 100% throttle and running "power" rich to maintain speed. I could lean it and adjust timing to run well and safe, but then it didn't have the power to sustain highway speed. Plan well. Are you really choosing the best option to reach all of your goals? Maybe. Maybe not. That's for you to determine, or discover.