It may be different in WA, and also different rules for camper trailers, but I do know that adding gas into a vehicle not originally fitted by the manufacturer requires inspection and sign-off by a VASS engineer. There were two guys lined up in the street when I was getting my engine upgrade inspected, and they had converted 10 seat passenger vehicles into campervans with kitcheneete's etc. For me, the VASS engineer inspected the installation plus the receipts for any components as part of the upgrade - no idea if they are that thorough in WA.