I have a 2010 F150 6.5 foot box with the max tow. The Payload is listed at 1960#. I changed the P rated tires to E rated 10 ply Nitto Terra Grapplers. I am planning on buying a 5th wheel to tow here are the specs for the two 5th wheels I am looking at. I will be buying a Pull Rite Super glide hitch that automatically moves the pin when reversing the camper (for short bed boxes). Any comments?

2010 COUGAR X-LITE 27SAB 1/2 TON 5TH WHEEL W/ BUNKS
Shipping Weight 6830
Carrying Capacity 3060
Hitch Weight 1090
Length (open) 29' 10"
Exterior height 11' 11"
Fresh Water 41
Waste Water 28
Grey Water 56


Rockwood 8287SS
Dry Weight 6,749 lbs. (3,061 kg)
Gross Vehicle Wt Rating (GVWR) 8,418 lbs. (3,818 kg)
Hitch Weight 1,418 lbs. (643 kg)
Length Feet 30
Overall Length 30 ft. 0 in. (9.14 m)
Exterior Height 135 in. (3.43 m)
Exterior Width 96 in. (2.44 m)
Wheel/Tire Size 15 in. (38 cm)

 

Superglide weighs about 150-200 pounds, so that's a hit on your payload. And the large storage under the front bedroom means more pin weight. Just keep that in mind.

I have not been impressed with any Rockwood trailer quality. Some Keystones are good, but not sure about the Cougar line. I like the Outback quality for example.

 

If I add a hitch to the back of the 5th wheel and put three bikes on the bike carrier does that add or decrease the pin weight? The Rockwood is basically out. The 380+ pin weight rules that one out.

 

It will decreases pin weight. Three large bicycles hanging off the back of the trailer should change the tounge weight something like 2-5 lbs.

Trailer axles are placed in a 6:4 ratio for balancing the load with 20% of the GVWR as tongue weight on a bed mount hitch style trailer. So a large majority of the weight from something hung behind the rear axle is going to be added trailer weight and very little tongue weight difference.
Be careful with this though. You can easily upset your balance if you start putting lots of stuff in the rear of the camper to try and carry more trailer weight without increasing your tongue weight.
This will cause a trailer and truck combination that can possibly loose control.

If you look at the numbers, the heavier Cougar already has a lighter pin weight. This means that added weight should be in the front area of the trailer to maintain that 20% for balance. It is already marginal for pin weight balance.

BTW, the Cougar loaded up after subtracting your hitch weight will exceed you trucks published limits.