I'm going to throw out some stuff here, and hope I don't get flamed to a crisp...
I just sold a Scamp 13' trailer that weighed in at about 1,500 lbs. When I bought that camper, I had a 2006 Honda CRV. It towed it pretty well, even at the SUV's max capacity. I kept the trailer pretty empty. It had electric brakes.
When I bought my T4R, I took into account the towing capacity, knowing I would upgrade my camper. At the time, I had no idea about the cross-member mounted receiver, which isn't really good for a WDH.
I am in the process of purchasing a Lance 1685, which has a dry weight of ~3,700 lbs. I KNOW it's going to sag the rear suspension, so I'm adding Firestone air assist bags. I plan on traveling with only about 10 gallons of water (<90 pounds), and keeping total gear to <500 pounds (~4300 total).
I can't seem to find the final word on WDH, but it seems like a bad idea for over torquing the cross-member without some leverage onto the frame. Maybe L-Brackets to join the cross-member and the frame would be good, so I may have that done in the future sometime.
I'll be towing the trailer through the Appalachian Mountains, so I expect I'll be using the truck lanes on uphill sections. I have a proportional brake controller.
I'll report back after the trip (if I make it). Kidding of course.
I expect to be actively engaged with the transmission....
Any thoughts or words of advice?