Dually valve stem extension on Mercedes Sprinters

I recently bought a LeisureVan Unity - Class B motor home on the Mercedes Benz Sprinter chassis and cannot check or add air to the rear dually wheels without taking off the wheel covers. I have found several companies that sell a metal valve extension kit where a tire shop would have to remove the tires from the rim and replace the original equipment rubber valves with the new metal ones.....supposedly getting them out beyond the wheel covers? Does anyone have any experience with this on the Sprinter chassis? How has it worked for you? Thanks for any info you can provide!