If they change a lot, you probably want to check them into version control to make sure that they are versioned... This way, you will be able (in theory, at least) to more easily reproduce an historic build if the need arises. If they don't ever change, you might consider putting them into some shared location on each of your build machines and pointing your projects at this shared location - this way you wouldn't have to worry about skipping the clean step (which is surprisingly difficult in V1) and could more easily use the same set of files for multiple build types.

-Aaron

No, it is not possible to do a "permanent delete" in v1. Deleted files will still be in the database and can be recovered if needed. A permanent delete is likely going to be in a future release.

Swaha