Thats why they make heatsinks out of ally!
Stability wont have owt to do with it though, the keel and hull affects that, if its a tub that is designed to be taken out of the water and trailered then the hull design will be flat, 'tunneled', or 'churched' making it less stable in the water.
One of the best smaller plastic - er fibreglass boats I've messed with is a wavey rider, reasonably good all rouund for what it is, but you cant beat a hardy for anything but racing, they look dull and boring but handle really well and get you through the weather.