Dear Jim & Bertie
Excel 5th wheels are built on a 10" x 2" box tube frame. Peterson Industries is the only 5th wheel manufacturer who has a frame strong enough to be endorsed by "Hydralift", the manufacturer of the motorcycle lift. If you go to
http://excelrvs.com/video_downloads.htm and click on the "Our Frames" you can see how our frames are manufactured.
As for the effect of weight, we carry around 2800# pin weight on most units. Since the axles are approximately 2/3 of the way back, putting your motorcycle on the back will decrease the pin weight by about 500-600 pounds according to our testing. Even though you fall out of the "optimum" weight-to-pin ratio, you are still quite safe pulling the fifth wheel. Most people tow full of fresh water, and with quite a bit of cargo in their basement storage areas anyway, so both of those factors also bring your pin wieght right back up.
I hope this helps a bit.
Thanks for reading our forum
Bryan Tillett