Here is a link on a project, the material is found at Lowes or HD is light yet when use as a coring material and laminated is as strong as it gets ..I will use this foam when and if I ever embark on a pilot house on my V.
Be sure to browse through it he did a great job testing and documenting everything.
http://www.shareaproject.com/pages/i...i,7971,00.html