Custom Marine Concepts in Spring built this rod holder for my Seaark. It's a permanent mount, but it is at the transom and doesn't interfere with anything when not being used. For my cap rail, which is extruded aluminum like yours, I used Driftmaster rod holder bases also shown in the photo. The cap rail is thick and plenty strong to be drilled and tapped for machine screws. The bases are drilled for #8 screws, but they could be drilled out for #10 if you think you need more strength. I didn't think I needed it.
You could put two Driftmaster bases on each side, close to the transom, and run two rods on each side in a spider configuration.
I wouldn't worry too much about having to cut out any of the flotation. I removed quite a bit to install these Plano tackle box holders on each side of the leaning post.
