re: Burial urn

When I made the urn for my mom, the ashes came in a plastic container (as you described) which I just slid into the urn.  Less than four years later when I made my dad's, the same place used a much larger cardboard box.  I had used the same design for both urns so we ended up merely placing just the plastic bag (which held the ashes inside the cardboard box) into the urn.  If your urn ends up too small, you can always pass out little containers of the extra ashes to other family members.  🤔 
L/W