I'm with Hooked. Buy 6' of 2x6 redwood construction grade lumber and take a grinder with a flap wheel to it. Shape it to fit the 2 depressions, and then mount your seat on top of them. It might take a little time to get it right, but when you're done, you will have a solid base and you won't damage your kayak. I'm planning to build a base for an elevated seat for Daveg99, but he hasn't brought it to me yet.
Dad took me fishing when I was 10, and I've been pretty much hooked since. He went to be with God on August 14, 2012. I miss you, Dad.