Welcome aboard ! First you measure under the seat area and then go to Walmart and buy a cooler that fits your space! You can handle that I'm sure.....thumbs up and good luck ! Let us know what you find...
I think mine was an igloo marine ultra cooler.
Roger
I can't help. I keep a rolled up dinghy under mine. One option is to remove the seat and buy any cooler you want. You can put a cushion on top and make that the bench seat.
If the main reason for this is supporting the middle, you can install a fold-down leg. We use our's only when we have guests, otherwise, it's tucked up and not even noticeable.