You should have them signed off by an engineer once they are installed and then get the seating capacity of the vehicle changed.
If you don't do this you may find your insurance is void.
I got extra seats installed in my Defender years ago (by the dealer selling me the vehicle) when I received the registration paperwork I questioned why it was still registered as a 5 seater rather than a 9 seater. The dealer ended up having to get an engineers report and resolving the issue. They claimed they had done this and VicRoads had lost the paperwork (quite possible knowing VicRoads) but I think they hadn't bothered to do it at all.
Colin
'56 Series 1 with homemade welder
'65 Series IIa Dormobile
'70 SIIa GS
'76 SIII 88" (Isuzu C240)
'81 SIII FFR
'95 Defender Tanami
Motorcycles :-
Vincent Rapide, Panther M100, Norton BIG4, Electra & Navigator, Matchless G80C, Suzuki SV650
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