Starboard or other material comes in sheets of 54"x96".
I used 3/8
material, but saw someone else use thicker and used clear acrylic rods drilled into the board to support his rock structurre.
I will building a rod system too but will have to surface mount the rods, which I think will be better so I dont have the holes to deal with later...
Thinner board will tend to warp and let detrius under the board.
You can silicone the edges but silicone dies not stick well, and will probably split in time, but it can help with the detrius in the joints.
Cutting it with a fine tooth blade and use acylic lubricant that you get at the plastic store, it is a 2x2 inch by about 1-" piece of some type of lube for cutting plastics. It reduces the friction and melting of the plastic.
Good luck
Bill