In addition to having a spare set of bearings and a dedicated floor jack for the trailer, you need to check the trailer spare to make sure its properly inflated and not dry rotted.
Also, I would think that you will probably get between half and 3/4 of your normal fuel economy while towing a boat. As someone said above, whoever is supplying the tow vehicle shouldn't have to pay for 1/3 of the gas, or if you did, then they should by you a dinner or something.