After reading a few thousand posts on RV.net, I think that most folks would agree with this summation. Disclaimer: I'm talking in very general terms here, and every trailer, 5er is different and has different weights. But as a general synopsis:
Travel Trailer or 5er total length 23 feet or less = 1/2 ton truck Single axle, gas or diesel
Travel Trailer or 5er total length 23 - 31 feet = 3/4 ton truck gas, but diesel is better, and single or duly, but duly is better.
Travel Trailer or 5er total length over 31 feet = 1 ton. You can do it with a gasser, but diesel is by far the way to go, and duly will give you much, much more stability. And still use a WD hitch system.
Anything with a triple axle or over 40 feet, you at the line where you need to start thinking about HDT trucks or 450, or 550.
Here again, this is VERY subjective, it does depend on the weights of the trailer and every trailer is different. And you can tow with any truck, but the question is, how comfortable? And... do you have enough truck to stop the trailer in the event of brake failure in the camper. (This will happen some day ... even if you simply forget to plug in the trailer pig tale to the truck one time ... like I did once, and on my previous trailer, had brake failure 3 times until I was able to get the problem finally fixed).
Regardless of the size of your trailer, get a proper hitching system and don't short cut.