Pat
Mechanically it can be done. But they are for sure going to have to go deep into the existing frame rails. Not just tap into the header. And the more I think about it, the A frame is in the way just behind eh header. Not easy, but not impossible. There is too much stuff under the TT to contend with on the frame rails. The fresh tank, the black tank too.
However, it will come with very high tongue weight. Right now I’m sure you could be at 1,200# maybe more when the motor bike is not on the back.
How heavy is the bike and side car you will be adding up front? You can add that right on the already 1,200# of tongue weight plus the extra frame weight. And your tongue may 1700 to 2,000#.
Reese does sell a Titian (Tow Beast) receiver. I have one and it is a 2 1/2” receiver. The Stock Super duty on the F250 and F350 with SRW drive is rated at 1,250# in WD mode which was why I upgraded as my T310SR comes in at 1,375 to 1,400#. Mine is only rated up to 1,700# in WD mode. However they now have even a heavier one. But then the F250 frame rails have to take it which might be an issue to overcome.
And then there is one other issue, the TT axles and tires. Unless you went on one serious camper diet, you may be out of axle capacity. The T2499 from Sunline put in 7,000# of axles and tires. This has to be kept track of to make sure you do not go over this. While tongue weight will go up, the TT axles take some of it too.
Actually after quick thoughts what you are describing is almost like a horse trailer. Wheels way in the back and one long trailer bed. However they are gooseneck hitches so they do not have to deal with the WD hitch and towing on the ball. And the frame under them could look more like a 10” I beam. Verse your 6” I beam.
Or, I know this may be out a little in left field, but it might be cheaper to get a custom gooseneck trailer with the right frame setup, takes the torque flex axles off the T2499 and slide the entire thing on the gooseneck frame that matches the T2499 frame rails. If they can position the axles in the same area as the Sunline, then the wheel wells will at least be in the right spot. You will also have to get a new step to get in with as the entire camper is higher.
Here is one custom gooseneck hit on the web
http://www.gooseneck.net/268623.html
Then some day you want to sell the T2499, separate the 2 and put the wheels back on and sell the gooseneck trailer and the T2499 separate.
I have no idea on cost but it will be mechanically sound
For the price of a new Tow beast receiver and a WD hitch in the 2,200# to 2,500# area yet to be found, (if they make one) a goose neck hitch in the truck bed is far cheaper.
Basically putting it, can what you are asking be done, yes. Cost, don’t know.
Good luck
John