Not to worry.
I have been carrying touring kayak or a solo tripping boat off-center for many thousands of miles. In N.America the Coriolis effect counters any tendency to pull to the left.
Not to worry.
That trailer had Tor-flex suspension but I don't know which one. The parts looked a little bit like the New Year's Eve noisemakers that have a crank on a flat round metal box. The owner's manual mentioned rubber bands or cords inside the axle but I don't know about collars. Trailer payload max was rated to 1400 lbs, if that helps you. I remember looking under the flatbed and noticing how much ground clearance the system had. Pretty impressive clearance, given that it was riding on little 8" wheels.
The new trailer has a much wider, lower axle, and I doubt storing a boat on one side will give it a list. Even without being in the middle (can't do that anyway cuz there are risers in the middle), the boat's weight is still closer to the center. The snowmobile trailer's flatbed actually rode on top OVER the wheels, which had a narrow track. Newer models of that trailer have the flatbed sitting BETWEEN bigger wheels, with fenders. I wonder if someone yanked hard around a curve, fast, and tipped the old-style trailer? Never was a problem with just kayaks on ours but might have been a different story if we'd stacker'ed 4 kayaks and had weight outside of the wheel track, or if we'd added a second level and made it top-heavy.
That was one tough trailer, though. I hope the new one does as well. One wheel already has play in it (didn't when I got it), and I haven't even used it on any road trips. The guys at the hitch shop said when they adjusted the play out and tested it, the bearing started to heat up, so they went back to the old setting.
From my bike wrenching days, I remember that top-quality bearings (Campy Record, whether pedals, hubs, bottom bracket, or headset) could be adjusted to have zero play yet still spin freely. None of the other conventional cup-and-cone hub bearings I've had has ever lived up to that standard. I have to wonder how good the bearings on most inexpensive trailers are. And yeah, probably all kayak trailers would be considered cheapies. Actually, I'm not too impressed with what I've seen of most boat trailers in general. Taillights and sidelights that stick out, inevitably to be bashed; crappy wiring layout; poor license plate fixtures/location.
I wonder how hard it would be to make a really, really good kayak trailer with all those little details well-executed, and super-durable including on rough roads.