In 2016 I did a CNG exchange at Longbeach LA. Once I got the boat to Seattle I converted to propane.
It was not a simple conversation. CNG tanks were stored inside the boat. The gas line had several joints in it. I ended up building a custom propane locker with all the safety equipment and running the proper certified hose.
On the plus side propane tanks are much lighter, last much longer and are a lot cheaper per BTU.