Our Cougar didn't have a sliding bumper, but the ones I've seen with it don't appear to have an easy solution to installing a hitch and keeping the sliding tray. There are a couple of "receiver kits" that will fit without the tray. One is offered by Curt Hitch:
http://www.curtmfg.com/part/13703
We had a local welding fabrication company install the receiver on our trailer. It's "custom welded" to our specific application. They also installed a similar receiver on our Springdale. Our trailer is 31' long , the truck is a "short bed crew cab" and with the boat hitched, we measure just under 74' long. So, yes, you're probably going to be "pushing the limit" in length, but it is certainly a "doable mod". It is extremely convenient to be able to tow the boat and camper without using two vehicles.
Honestly, the rear of your trailer is the "roughest ride" of the entire rig. We tow a 18' bass boat behind our fifth wheel on most summer trips and when we don't, I have a Harbor Freight aluminum cargo rack, but it's never been on the trailer except when I put it together and installed it to make sure it fit. There is a warning in the Curt Hitch manual that warns not to use the receiver with a cargo tray without additional straps/braces to prevent the stresses from bouncing.