Rather than get an adapter for the Companion model, consider purchasing a marine 30A extension cable with twist lock connectors on each end. Note, this won't work for 50A trailers.
You will then be able to connect it directly between your trailer and Companion without need for an adapter.
Plus, it can be used as an extension for your regular power cord when the need arises.
among others, makes these. While a bit pricey compared to a normal RV 30A extension cable, you can make the connection between your regular power cord and the extension cord waterproof and secure with a connecting sleeve and ring.