Originally Posted by ruscal
They're both very significant, but come into play in different ways. Weight
matters most while climbing, as it takes more fuel to lift weight
up a hill. Wind resistance matters everywhere, and becomes more significant with speed. Hold a ping pong paddle out the window at 20MPH flat to the wind and see if you can feel it. Do it again at 120, and you may get hurt. We cyclists know all about the effects of wind resistance and energy use. It is very significant at almost any speed and the largest drag bicyclist will experience. Heavy bicyclists know all about how weight
effects climbing hills.
Slow driving will affect MPG always. Heavy vehicles hurt climbing.
I was speaking to "aerodynamic shape
" alone, and specifically within the limited sphere of camping trailers and the average speeds they travel at.
For decision-making purposes, at least for me, there's not enough variation in shapes among trailers to make significant differences in fuel efficiency, especially over the relatively small distances most travel.
Surface area presented to the wind is of course another story...