Use the travel trailer (TT) gross trailer weight rating (GTWR) as what you will more likely be pulling, then figure 13-15% of the GTWR as tongue weight. This will help prevent you from overloading your tow vehicle (TV). Don't forget to subtract the weight of the Weight Distributing Hitch (WDH) from your TV cargo carry capacity.
Yup, until you have the TV & TT on hand for actual measurement, it is all a math excercise using factory specs to make the best guesstimate in choosing a TT.
TT factory specs may be true but are severely incomplete. The dry weight is nowhere near the ready to camp weight. The speced tongue weight is based on the dry weight leaving the factory, no battery, empty propane tank(s). Also, part of the GTWR is what gets carried as tongue weight, at least on single axle trailers. Example: My TT has 3500# axle with a GTWR of 3877#, factory tongue weight 377#, 3097# dry weight, CCC 780#.
2019 Cherokee Wolf Pup 16BHS flipped axle
2019 Ford F-150 S-Crew 5.5 bed V8 w/tow package, 3.55, 7000# GVWR, 1990#CC
Husky Centerline TS WDH 400-600# spring bars