Question on Re-installing Dining Seats and Bunk Bench

[Kirby]

Hello All,

So excited to be a part of this forum. I've already learned so much about our little trailer from all of you. So, I thank you!

Here is my question:
We recently purchased a 1975 El Macho (which is the American version of the Boler) and the dining benches and bottom bunk portion were removed to paint the interior. My husband and I are trying to figure out the proper channels to re-install these correctly. There appears to be a lip that the furniture sits on and we cannot tell what it's made of. I have attached some photos for clarification. Any input is greatly appreciated!!

Thanks again!