How much steel did you put under the floor to support this deal? (any photos underneath) I can only assume you do not intend for the plywood floor to hold the weight of two Harleys?
This, strength wise would need at least a piece of steel twice the size underneath that is showing above floor, and the crossmembers in the newer motorcycle trailers are paper thin so they also would not hold the weight of the bikes,
I cannot imagine using this without tiedowns, really scary. At least the tiedowns would spread the weight and resulting pulling forces around the unit instead of just one spot.
I looked at this deal in Daytona a few years ago and asked the guy what you were supposed to do about support, he asked me why? I was amazed, he also laughed when I asked if anyone had done any mechanical calculations as to support and bracing. He then chose to walk away and take a break.