[HumblePie]

We had good luck with a composite material that was 2 thin sheets of aluminum (about .010" thick), bonded to either side of a corrogated plastic core. The trade name is "Alumalite" and it is used in the signmaking industry. It was very light, and had good stiffness. The only downside was that the corrogated core would collapse under concentrated loads. We used this material for our belly pan, so the solution to the point loading was to use c'sink head screws, and they would self-countersink as we tightened them up, being careful not to over-torque them. Velcro also worked well to avoid the issue.

We also used it for our shooter deck sandwich. It was light and lent itself well to waterjet cutting. Later, we found that there is a solid polyethylene core version called "Alupanel". It solves the point-loading problem, but is a good bit heavier than the corrogated core. Both are available through sign shops (always ask for donations, they may have cutoffs) or online.