As far as diamond plate. Bare dp gets hot to the touch! It is also not flat so seat bases or mounting stuff may not sit flat. I'm not sure what coosa board is but those are my experiences with dp.
I like dimond plate, but as pointed out its a bit hot but some carpet would sort it tight out.
I prefer flat aluminum with carpet as the best of both worlds, thats the best I've ever had, stronger and permanent.
Can get heavy but so does a lot of plywood.