Small platform for battery and storage box- what type of material?

I am putting together the small CC for my boat, which I am using a console from an inflatable boat company. The CC is made from aluminum tubing and I want to add a small platform in the legs to store my battery box and dry storage container.

I am asking the best material for this. I was thinking marine ply epoxied but figured that might be a little more work than necessary. The box will be sat on occasionally and loaded with a battery and wiring. Sometimes I might just put a cooler on it when I dont need the battery- so it has to withstand a little bit of weight. Is starboard good enough? If so what type and thickness? The platform will be 22W x 18L, or there about

For reference I tried to attach a pic:

Let me know what you think

 

Thanks, thats what I was thinking. You wouldnt know any websites that sell it like that would you? Im pretty new to this type of stuff and wouldnt know staboard from a lesser brand really.

Also, do you think this is a decent idea?

Thanks!

 

Im in South Florida.

Thanks, I saw that site. Do you think 1/4 is strong enough?