The wellnuts/screws on a Hobie Adventure can easily be used as mounting points. I used the ones near the front hatch to fasten a polycarbonate shelf for my fishfinder base. When I changed from a Humminbird to Garmin, no big deal; I just drilled new holes. Polycarbonate is very strong and will not crack like acrylic.
I made aluminum mounting plates for the ones behind the seat. These are used to support the pvc rodholder I made. The plate provides front-to-back stability while the V construction provides side-to-side stability. Other features that I like of this rodholders design is that they are angled at about 45 degrees, they have a low center of gravity, the mass is kept close to the centerline of the kayak, and the rods are within easy reach.
In addition, they point slightly forward or back, depending upon which direction they are mounted. When pointed forward, the tips of the rods can be seen without much effort.
I also built some extension tubes for the builtin rodholders. I use these for my bass rods. Electrician tape wrapped over one layer of corktape on 1 1/4" pvc creates a snug fit. Instead of using lanyards to secure the rods, the bungies are looped over the reel handles.