If you look at the carrier I ordered, you will see the manufacturers tie down system. I would be concerned about unexpected bumps at railroad crossings, bridges, etc. My concern would be losing the bike, maybe causing damage or injury to traffic behind me.
I just returned from a 1,000 mile trip, pulling a second trailer, with my dirt bike, and FZ1 canyon racer on it. I encountered a pavement drop off, no warning, just a sign saying construction ahead. Nothing came loose, but sure could have.
Normal driving on fairly smooth high way, I think I could get by with the carrier and dirt bike. I would strap the wheels, as well as the bike frame, and bars. My FW receiver looks very solid, with 4X4 square tubing running across to the frame. I will know more when I get the carrier this coming week.
I really think the 300# FW receiver max, is due to them not wanting any more weight, that far behind the axle.
I have no problem with the truck, and bouncing, it was ordered with 350 suspension, and tows the FW very nice.
Hope you find a solution, that works for you,
Jerry