The way the Lund Sport Trak works is you buy the Sport Trak Adapters, they are approx a 4″ x 3″ plastic ‘puck’ that has splines on the back that fit into the track.
Then you buy virtually any rod holder from virtually any manufacturer you want, and attach it to the adapter, and insert the adapter splines into the track to attach it to the boat.
So take your pick. Find any rod holder you want basically. There are dozens and dozens from numerous manufacturers.
Here’s a video that explains how the system works:
You should also note that the brackets come in both straight (90 degree) and angled (45 degree) versions – you need to get the correct ones to match the track on your boat, some of them use the angled and some don’t.
There’s also other 3rd party brands that are just as good (or better) than the Lund ones at significantly lower cost. Extreme-Max is one:
Depending upon how simple and easy you want, the Sport Trak brackets should work fine for basic trolling rod holders. Now… if you choose or desire a bit more “beefy” system for your tube holders, accommodating two or more rods? I can recommend using the Sport Trak downrigger bracket attaching the rod holders to an aluminum (easier to fabricate) or stainless plate then attaching that plate to the Sport Trak downrigger bracket. The Trak anchoring slide can be slid to the stern and allowed to stay in the Trak with thumbscrews snugged and the holders can be removed and stowed out of sight and away. This helps for covering and trailering purposes.
The extreme max ones are great, I love them. They come with both a thumb set screw and hex key recessed set screw, so depending on your application you can put a plate in a more permanent location or make it so it’s adjustable.
I have “broken” two of them, running my rod holders into trees. They still work fine but the insert piece cracked. It feels as though they were designed that way to avoid breaking the rod holder. Never had a fish come close to breaking them.