Knowning the dry weight is very important when buying a new RV. If you don't know that number, how will you determine the actual carrying capacity of that rig? Some TT have a real close weight between the actual dry weight and the GVW. By the time you add the LP, and full fresh water you don't have much capacity left for your items. It is great to have over 4,000# capacity over the dry weight, but that is the exception for most rigs. The numbers between the dry weight and the gross weight are very close on many rigs.
