I thought I had written or described this before. When our trike was built, being a Lehman GTL, it had a hitch or draw bar that was a piece of chrome flat steel with a "S" to raise the ball area. It was springy. Not suited to much of a hitch rack, but very capable pulling a trailer. If not for a hitch rack, I think the flexible springiness of the OEM flat bar draw bar is best for simply pulling a light weight MC type trailer. The flat bar absorbs and cushions shocks jerking up or down.
While at a rally one day, I noticed another Lehman GTL there, silver …. with a receiver. I looked under it, saw his was a zig zag cut & welded tube that bolted to the two cross members under the trunk. I figured that it was at least as capable as the stock drawbar, but not enough for my hitchrack idea (keep in mind, when I built my house, I never used just 2 16Ds where 4 would fit). I have no recollection as to what he towed.
If doing it today, I might follow his lead with the install of the receiver portion (his was clean in design, but I have yet had anyone crawl out from under mine with a negative comment as to my hitch or receiver's looks) …. but I'd still add my brace idea up to where the center stand once was mounted as without the brace, it can place additional stress (from forces of braking, pulling, & weight simply pulling down) on the trike frame where it goes over rear axle and then drops back down. The brace must be shortened or stretched by the forces if the rear of the frame flexes, which I think unlikely.
I built mine to quickly set in place of the removable long chromed flat bar. Then, I built my hitch rack, and it seemed to me that the weight of a load on the new rack was pulling down on the rear frame, like a lever. So I built a cross bar with 1/4" thick tab in center to mount in the brackets once used by the bike's center stand, then I cut a piece of 1x2 steel channel, partially boxed it, and bolted it between the tab up front on the new cross bar, and the receiver. Maybe not needed. I have a wood block cut to straddle the 1x2 and fill the space from 1x2 up to rear pumpkin, it jacks nice as the rear axle supporting suspension and trike is jacked along with trike, etc. The round holes in boxing strip are where two more bolts tie into receiver. I cut and sectioned my drawbar, it was one I was given, I welded in a tail skid (keep thinking I'll change it to a small wheel) too that will catch a curb if backing before exhaust tips do.
Anyway, just thought maybe someone else is thinking or looking for ideas. Pardon road dust / grime. Last picture is that silver one I saw. My hitch carrier has it's own welded 1.25" square bar, I use 1/2" pin and a 3/8" bolt to lock in place with no rattles or rocking. Had a buddy sit on it as I was underneath (trike on ramps), no movement in chassis, just rear shocks. My hitch rack has lights I plug into trailer plug. I do still have the Lehman chrome flat bar drawbar too, it would be easy to reinstall if desired.
I do clearly recall the once popular carriers made from leftover saddle bags after trike-ing a bike. Haven't seen them used lately though. I was given … and still have … our trike's OEM saddle bags with matching pinstriping from when it was trike-ed, (CR then had rear of new trike re-pinstriped to match front bike part, we had it all touched up by same fellow in 2005 and added some small details, like Abby's pic on trunk) but I just thought they looked a "bit much" in rear overhang so they still lie stored above the carport. I do have drawings for the frame to mount the saddle bags as either a carried carrier, or a single wheeled trailer with two hitch points and a single caster wheel to follow the trike. If I did use them, I think I'd favor the latter means …. but then I ask myself "what to do at the motel when day riding?".