We had a memorial service last week for a former pastor and his ashes were in a simple unstained square Oak urn with some decorative laser engraving on one side. Looked like a simple workshop project except for the laser work which should be easily shopped out. I would pick out a small standard plastic screw cap container and build an urn around it. Rockler has what they call urn hinges. At your request, they will provide the ashes in a special plastic bag in a cardboard mailer, and you can take it from there.