You should also make sure your vehicle of choice is tuned and you have the proper air pressure in your tires, that includes the trailer tires.

Inflate to proper pressure while tires are cold. I'd make sure your vehicle's air cleaner filter is clean and for a few bucks invest in a permanent type that will increase air flow, resulting in better fuel economy. A new PCV valve and gas filter isn't a bad idea either, maybe a new set of spark plugs as well. All easy enough with minimum mechanical ability.  Also make sure you O2 sensor is working good. There cheap enough, if in doubt, install a new one.

Last but far from least, don't let the lead footed brother drive, unless he wants too pay a larger share of the fuel costs ;D