I've got a few mods planned before hitting the road for the summer.
I tow with a '14 Toyota Tundra, and will add a set of Firestone air bags. With the smaller 189FBR, I didn't bother mounting the bags on it, though I did have them on the Toyota Tacoma that I'd used previously.
The shackles on the leaf springs will get an upgrade to a heavy-duty set, as well as wet bolts for easy maintenance (and fewer squeaks).
Over the bed, I'm planning on swapping in a Maxx Fan ventilator (with remote) to replace the wimpy stock fan. I'll leave the stock one in the bathroom for now, but will likely add a remote-less Maxx Fan back there later. Those things move some air, and are generally quieter than the stock fans. I also like that I can leave them open while on the road, and in any kind of weather.
I'm still debating on whether to swap out the new original tires for a set of Goodyears before I go. I had good luck with them on the previous trailer.