Wow, that is a tough one. You definately want all four screws mounted because there is a lot of torque on the mounts when you are bouncing a 12 lb weight at the end of a 30" arm. You also need to be able to reach it easily to raise and lower, which you will do a lot. There are some gunnel mounts available from Scotty that you might be able to make fit on the vertical side of the boat under the padding with some modification. There are also some aftermarket pedistal mounts that might have a smaller hole pattern. Check Outdoor emporium, Auburn Sports, Teds and bring measurements. They might have some ideas.