Yeah, "tow ratings" do not necessarily equate to travel trailers... Boats can weigh a lot, but have pretty low tongue weights. So, there you go right there..
Travel trailers/5th wheels have a lot more tongue weight than boats, so that's where the "rub" is here...
At the end of the day, you'll get down the road no matter how much weight you put on your truck... You just gotta decide what ratings and what other factors you choose to abide by..
I tow what I tow with a truck that far exceeds any of the weight limits of my RV.. Why? Because that's what I prefer to do after towing all sorts of things over the last 35+ years I've been driving and towing stuff for work and for pleasure..
The max GVWR TT I'd go for with my current truck would be #7500... Is that leaving a lot on the table? Sure... But I don't need that much in terms of TT and I want to enjoy the driving time as much as I want to enjoy the camping time... :)
No one but YOU is going to be behind the wheel of your rig, so in the end, it all boils down to what you are comfortable with.. Not what us "interweb goofs" are comfortable with.. :)
Good luck!
Mitch