On my Nacra 6.0, (same as 5.8's etc.), I use a soft sided, well insulated cooler sold commercially.

I tie it to the Over-rotator traingular shaped bar that's on the front of the bottom of the mast!

Always out of the way completely, EASY to get to while underway, [color:"yellow"] [/color] without altering your boat trim by going aft to get in those ispec. port holes.

If you're lashing things down, of course take into accout things such ease of getting to sheets and rigging, boat trim, etc.