What 5th wheels have strong frames for double towing?

I first need to figure out what companies are pretty decent, then need to start calling them and asking about their towing capabilities. I didn't realize though that most of them are limited around 3k lbs. reinforcing wont be a problem. The trailer does have brakes on it as well. And that is a good point about the double trailer taking weight off the pin of the 5th wheel.

Sofar I have Arctic Fox to research. I heard the name fleetwood, are they a decent company? Any other names come to mind?