We use something like this in our aft berth under the cushion that was next to the engine, do not know how it would work for cold.
https://www.amazon.com/Reflectix-BP48010-48-Inch-10-Feet-Insulation/dp/B01M0G1PCA/ref=sr_1_7?s=hi&ie=UTF8&qid=1479162294&sr=1-7&keywords=reflectix+bubble+pack+insulation