I have a small Harbor Freight trailer that I used behind my trike when traveling around the country. I've had it configured different ways, according to my needs, from having a cartop carrier to having a frame of 80/20 extrusion on top so I could carry my wheelchair, and just a flatbed with tiedowns. A couple of things I highly recommend doing; replace the hardware with high-quality stuff, not the typical hardware store variety. I used stainless steel. And exchange the wheel bearings it comes with to a quality set like Timken. They're metric size, but still available. I can't think of the part number off the top of my head, but it's best to check yourself anyway, as they may not be the same. They made a huge difference in smoothness, and confidence. I removed a leaf from the two-spring pack. They're horribly over-sprung, and one leaf has cut out most of the bounce. I put a permenant tag on it when I licensed it, and now I can take that tongue and lic plate and put it on any other trailer I might build. I'm considering a small trailer build of 80/20 aluminum extrusion with torsion axles. It would be completely adjustable for size, and modifiable in almost any way.
On my boat trailer, I also went to plastic overlays on the runners, as my boat was difficult to load. It was a good change. I also went to oil hubs for long distance travel, and those worked excellent. They kept the spindles cool no matter how fast or long I pulled. That meant no water ingress at launch. Of course, they won't work on the HF trailer unless you change the axle.
Something else to think on; the less runners under a boat, the easier it is to load. But if you're traveling a great distance often, more runners will support the hull, and whatever structure is immediately above it, better. On thick aluminum with nothing inside, it doesn't matter so much. On anything else, it kinda does. An option is to have fold down bunks that you can raise after the boat is loaded. As long as they're the exact height needed, they can even be carpeted. You can use a lever to raise them in place if there's a lot of flex in your hull.
As far as the Flip N Easy folding trailer tongue, I don't foresee any wear on that pin if it's built right. There's a bit of tongue weight holding down on it, and the joint should be built with some slight tension on the pin. If there isn't, a rubber bumper or stiff spring can be added on the front side, so that you have to push down on the joint slightly to push the pin in. And the pin and hole should be smooth and sized for a close fit.