They will measure your trailer its one of the things they will fuss about one year a guys did not make the cut and he had to buy one,,,,,,,,,,, wait for it,,,,,,,,, yeah you got it he made it 15 miles down the road before he dropped a valve and was out.
Each competition vehicle may tow a single trailer up to 12 feet long from ball to tail and 6 feet high from ground to top, including the height of anything carried on top of the trailer. Alternately, a U-Haul 4x8-foot box trailer may be used. Trailers may not contain any components that contribute to cooling, charging, oiling, or fueling the competition vehicle while the trailer is being towed
.....but, I also only ran one set of tires for the week, and ran on pump gas. No need for extra race tires (although I did have one extra matching front AND rear wheel/tire on board as spares) or race gas to haul around. I did bring my four year old in '05 and again in '06. Hell, I must have had 50 lbs. of hot wheels on board!.. plus all of the other things to keep a little one buisy.