Thank you for the numbers!
The UVW is the RV weight as it left the factory. The weight of dealer installed options are not included. If this number is from literature, then factory options may not be included either.
Assuming UVW is correct, GVWR is the most the COACH can weigh when it crosses a scale. In other words, you may add 3400 lbs of food, water, clothes, tools, lawn chairs, toys and people AND TONGUE WT. (See below.)
GCWR is the most the coach and whatever it is towing may weigh. If the coach is loaded to capacity, then any toad or trailer is limited to 4,000 lbs. HOWEVER, If the coach is only carrying 2400# of stuff, then you can handle a 5,000# toad. 26K GCWR minus 21K actual coach wt = 5,000 for a toad.
You must meet each weight limit, but if one is less, the other may be more.
The coach brakes are intended to stop the coach ONLY! Any toad or trailer over about 3000# REQUIRES SEPARATE BRAKES. This varies by state. Some are as low as 1500#, most are 3000# or less. You must abide by the laws of the state you are in at any given time. Toad brakes are required by most state laws, required by the laws of Physics, and required by the rules of good sense.
**Tongue Wt ** Any trailer or toad will place weight on the back of the coach, on the ball. This becomes part of the weight of the coach. For a conventional trailer, this will be 10% - 12% of the weight of the trailer. For a toad, it is only the weight of the receiver and part of the weight of the hitch - less than 100# The toad "carries its' own weight" with respect to tongue wt.