The gross weight in the case of any motor truck, tractor, or truck  tractor shall be the scale weight of the motor truck, tractor, or truck  tractor, plus the scale weight of any trailer, semitrailer, converter  gear, or pole trailer to be towed thereby, to which shall be added the  weight of the maximum load to be carried thereon or towed thereby as set  by the licensee in the application if it does not exceed the weight  limitations prescribed by chapter   46.44   RCW.  If the sum of the scale weight and maximum load of the trailer  is not greater than four thousand pounds, that sum shall not be computed  as part of the gross weight of any motor truck, tractor, or truck  tractor.  Where the trailer is a utility trailer, travel trailer, horse  trailer, or boat trailer, for the personal use of the owner of the  truck, tractor, or truck tractor, and not for sale or commercial  purposes, the gross weight of such trailer and its load shall not be  computed as part of the gross weight of any motor truck, tractor, or  truck tractor.  The weight of any camper is exempt from the  determination of gross weight in the computation of any licensing fees  required under RCW  46.16.070.