I printed this spacer to take up the extra room in the battery box of my RV4 when replacing the Concorde lead battery with the EarthX Lithium battery. Spacer dropped right in with a bit of room all around.
https://www.printables.com/model/611684-vans-aircraft-rv4-battery-spacer
https://www.printables.com/model/611684-vans-aircraft-rv4-battery-spacer