Water noodles are too soft and flexible to use. It does make a good shock absorbing material for make nose pods out of, though...

White Styrofoam, EPP, and 'Pink' foam (from the local building supplies house) can all be cut with a hot-wire set-up.

Fan-Fold BluCor (also from the building supplies house - depending on where you live) and Depron (DepronUSA.com) or balsa can all be used for very light weight built-up structures. depron seems to be lighter and more resiliant than blucor, but costs more.

Check out the Profili link I mentioned. The trial version is free, and $10 unlocks all the features. You can generate templates for cutting the foam cores (or ribs, complete with spars, etc., if you choose go that route) very easily with it. It is worth a download and a look...