Chris, my ER25 collets came in a wooden box with holes for them to sit in, but this glorified pipe-rack I made for general taper tooling might give you ideas

It's made out of cheap white HD polyethylene kitchen chopping boards (I used old, scratched ones), sawn up and held together with self-tappers. It has a solid back, to keep it squared up.
HDPE is easy to work, won't scratch collets like metal might, and doesn't give you splinters like wood.
Andy