Re: Does anyone know how to......
Noah, time to get the drill and brackets out, metal or glass boat?
Even simple right angle brackets to slip the cooler in, as well as the bungees Jacob recommended, should secure it.
I guess you're holding up to a couple hundred pounds of fish, so you should bolt the brackets through, and reinforce the area underneath the cooler with plates or large washers where you bolt it through, and make sure where you drill doesn't weaken the transom or rear deck area, or interfere w/any other systems back there.
I'm assuming limits of up to ?? 3-4 people per trip?