I've never used balsa as a core material, however I'm very familiar with balsa from other hobbies.  I'm thinking it may be my best bet as a core that needs to be shaped. I know I'll have to drill it.  What else do I need to know that is different from a cloth or honeycomb based core?

You can use flat balsa as it comes from a hobby shop, it is just not the typical way with composites.




When people refer to balsa core it usually refers to the type (end grain balsa) that is supplied as small blocks held together with a scrim layer on one side. This way you get the advantage of the end grain strength in the sandwich.




Personally I avoid using balsa, being a natural material it can absorb moisture before you have even used it, and then that moisture will inhibit the cure of the resins bonding to it. If the bonds are not good then you can serious problems down the track. Foams are much lighter, more predictable and safer in the long run.