Buy a Down East dual clamp Salty S-10, or a S-17 bolt on. Best rod holders for musky trolling period. I troll baits up to 21" long at 6mph and I have never had a problem.
If I were you I would spend the $35-$50. The last thing you want with a 30lb musky on the end of a line is trying to get a bungee cord off your rod. The S-10 and S-17 allows you to angle your rod anyway you like. This is key when you are precision trolling for muskies.
When mounting the rod holders try to mount them near the back of the boat if possible. This allows for making sharp turns easier without running over your line.
Goodluck!