How to determine hitch weight capacity

...when nothing in the door-post or the manual even mentions it?

We know the hitch-weight of our TT, but when shopping for a TV, how can you know the maximum hitch weight it can take?

There's nothing in the B-post labels about hitch weight maximum, and there's no mention of it in any of the manuals we're looking at. They all say that the hitch weight should be 10-15% of the total weight of the TT, which we already know, and we know how much our hitch weighs, but we're not finding anything about whether or not the TVs we're looking at can handle that weight.

Good for you for doing your homework. Many don't. This value should be well within the payload of the truck, that is a number you can find. But, if you are really concerned then as mentioned above go to the scales and be sure you are at or under the gross weight of the truck with all your stuff, people, dogs, kayaks, tools, fuel, spare parts, firewood, bbq, bicycles, and, or course, the trailer's tongue. If you use a weight distribution hitch it is important to remember that about 20-25 percent of the redistributed weight is transferred back to the trailer's axles/wheels/tires.