Average gas mileage?

What's your average gas mileage in your van or box van?

Also what your average if you're pulling a trailer?

I have a Chevy 2500 cargo van and get 14 miles per gallon on the highway without a trailer. I only get 9 miles per gallon when I'm pulling a trailer.
I'm thinking about getting a box van that can hold the truckmount portable and other tools we use when we travel. I'm just unsure if it's worth it. I'm trying to save on gas?
Thanks in advance for the input.