Start with the most limiting factor of 1620# payload for your truck. The max tow numbers are nonsense.
Subtract all the weight that is going on/in it.
1620 - 575(family) - 100(WDH) - 300(stuff in bed,firewood, bikes, generator) = 645#.
A TT needs 12 to 15% tongue weight for safe towing.(ie to prevent sway)
Divide 645 by .12 = 5375.
Divide 645 by .15 = 4300.
A TT to look for is in the range of 4300 to 5375# all loaded up to go. A family of five will easily pack 1000# or more into it. You should limit your searches to a dry weight of 3500 to 4500#.
As an example, I see a Keystone Passport 280BH with 2 fullsize bunks has a dry weight of 4590#. Add 250# of water and 40# of propane and it's up to 4880#. Fill up the front storage with tools, hoses, cords, chairs, etc and the tongue weight goes up fast.
My Bullet 295BHS started out with a dry wt of 5648# and a capacity of 7800#.
It was at 7300# on my last trip with 1100# tongue weight. (I upped the 20# propane tks to 30's, added a second battery, and replaced the cheap short queen mattress with a 10" standard queen memory-foam(heavy) mattress.) I also tried to limit the amount of water I carried to only 10gal while traveling. So keeping the weight down for a family of five will be a challenge.
