There is lots of useful information above. I will try not to repeat. I want to define some terms for you.
The published max trailer weights for older trucks, before the new standards took effect, assumed an empty truck and a 150 # driver, This is simply not the real world. The new specs are better, but...
PAYLOAD, or the maximum weight you can carry should be obvious. This will include all passengers, pets, cargo, purses
towing hitch and TT tongue weight (TW)
GVWR, by definition is truck curb weight + payload, and is the maximum the loaded truck can weigh.
For Travel Trailers (TT), the Dry Weight is what it weighed when it left the factory. IT IS MEANINGLESS. You need to use the actual weight packed and ready to go camping. Since this is not easily obtained, use the TT GVWR.
To tow properly, the TW should be between 10 - 15% of the TT weight.
Gross Combined Vehicle Weight Rating (GCVWR or GCWR) is the most your loaded truck + loaded trailer can weigh. If estimating, do not include TW twice.
A simple rule of thumb: Determine your PAYLOAD. Subtract all weight to be carried by the truck, as above EXCEPT no TW. The remainder is the maximum TW you may carry. Take this number X 8. This is the max TT GVWR you should consider.
WHY? Assume an 8,000# TT. 12.5% TW = 1,000# If the vehicle can handle 1,000# TW, then 1,000 X 8 = 8,000# TT wt.