I know you are most likely looking for something in a color mach, but for the cheap and dirty. Have a look at the Piggy. Basic Black, good setup, 18 CF load, light, and can be painted. and all for around $650.00 or so. I got this one while I was still on a GL1200 and had no problem. I have added the lights on the rear, along with other things in side. On my last trip to Ark I didn't have room for the "sink" but had every thing else, " Packed Heavy @ 545Lb " didn't know it was back there.
While the wide trailers do not have much impact on the rear axles of trikes, it must be understood that wide track trailers make an already bad situation worse on the basic GL 1800 rear frame.
Trailers that have poor compliance in the suspension, yank the hitch sideways, applying a load in a direction that is impossilbe to do with the bike alone. That being the case, the bike frame design has no stiffness in the lateral direction other that the inherent stiffness required for the vertical and fore and aft loading.
When these yanks are significant enough to be felt in the handlbars, it is getting into the fatigue spectrum of the frame. Fatigue is just that. It takes a while to generate enough cycles to start cracks. Many, if not most riders do not ride enough, and on enough rough roads, to actually break a frame, although there have been a few. The breaks due to this type of fatigue occur just behind the passenger foot rest attach casting.
It is bad enough to have trailers with low compliance suspension and with the triangle between the wheel contact patches and the hitch is less than 30 degrees included angle, but wide track trailers make it much worse.