Getting back to the OP's topic...
I am also planning on double-towing this year. My Jayco has the full I-beam frame and I found a hitch application that just might work!
The Curt #12923 is a frame-mounted receiver hitch that is adjustable to several widths. It has a 3500/350 capacity that will work in my circumstance. My second tow is a small Shorelander single jetski trailer that weighs about 1200# with the ski on it, so not much there.
My concern now is wiring a 4-flat into the trailer's brake lights. I haven't dug into it yet, but I can't find access to the wiring harness. It's behind the wall somewhere.