You've gotten some good advice in this thread already (crash is REALLY good at putting this stuff into words), so there isn't much I can add. It all comes down to weight, and sure there are some big trailers with low weights (I have a 35 ft TT that has a GVW of about 8500, we don't take much with us so I know it's nowhere close to that), but that kind of length compounds your math because it's a BIG FRICKIN SAIL. Wind pushes a light camper around more than a heavy one.
Things to consider:
1. The longer the trailer, the more it wants to sway. A longer tow vehicle will combat this somewhat, and a sway control system is a must. It can be integrated to your WDH or stand-alone, the choice is yours.
2. The lighter and shorter the trailer, the better it will feel behind your truck - as long as it's a double-axle. I've seen far too many single-axle trailers bobbing around behind vehicles because they're losing traction on rougher roads.
3. The integrated brake controller (not sure if you've got it) is a thing of wonder. There are some aftermarkets that are pretty good, but the integrated one actually applies your trailer brakes in proportion to your truck brakes instead of relying on a pendulum.
4. Remember that (normally) you're going to be pulling the trailer to have a good time, not make great time. You aren't trying to race to your spot, so slow down, take it easy, and pay close attention to your surroundings. I never tow over 65 mph unless it's an emergency maneuver, if people behind me don't like it they can pass.
5. Invest in tow mirrors, either OEM or aftermarket but you've got to watch it with aftermarket - some of them don't hold up. You'll thank yourself with the ability to see around whatever you're pulling.
That's about all I've got right now, I'm sure others will chime in.