gupd files are a good way to package files and let it automatically download on login. But please make sure that you specify the good path for files: they must match the path where it would download them by default (we can may be let it ignore the path in the future, but right now please specify the good path):
Images starting with something_ must be put in levels/images/something/:
levels/images/era/era_*
Heads, shields etc. in their levels folder:
levels/heads/*