Some info I have posted over on the FB/EK forum, edited to suit your situation.
Both my FB sedan and my EK wagon have seatbelts, fitted by me.
For my FB sedan I have non-retractable lap/sash belts in the outer positions, and lap belts in the centre. I have this in both the front, and the rear.
For my EK wagon I have retractable lap/sash belts in the outer positions, and lap belts in the centre. I have this in both the front, and the rear. For the rear, I mounted the reels on the wheelarch, and put the sash guide on the "C" pillar.
My understanding in NSW is:
a) if you are undertaking modifications that require an engineers certificate, then seat belts must be installed for all seating positions. Lap/sash seat belts are required for all front and rear outboard seating positions. Lap/sash or lap belts shall be fitted to inboard seating positions. The level of safety provided by seat belts must not be reduced. Seat belts must not be replaced by belts of a lesser standard or with second-hand belts. For example, lap only belts must not be used in place of retracting lap/sash seat belts. This is based on the NSW RTA Vehicle Standards Information Sheets No 6. for light vehicle modifications. My wagon went through this process, and has a full VSCCS (engineering) certificate. As Rob notes, it is not cheap.
b) if you do not require an engineers certificate, then you do not need to fit seatbelts. However, if you are carrying kiddies, the following apply:
Children younger than six months must be secured in a rearward facing restraint.
Children aged six months to under four years must be secured in either a rear or forward facing restraint.
Children aged four years to under seven years must be secured in forward facing child restraint or booster seat.
Children younger than four years cannot travel in the front seat of a vehicle with two or more rows.
Children aged four years to under seven years cannot travel in the front seat of a vehicle with two or more rows, unless all other back seats are occupied by children younger than seven years in a child restraint or booster seat.
I understand that the above child restraint laws are retrospective (i.e. that they are not "grandfathered" just because the FB/EK came out with no belts orginally). You would need to fit belts to meet the above.
c) if you are installing belts not for engineering certificates or for child restraint (but more for peace of mind,as is your case I think) then you can choose which positions get belts and which don't.
d) Any installed seatbelts (even the peace of mind ones) that are not subject to full engineering must be approved by an RTA Authorised Restraint Fitting Station. This is not an engineers certificate, just an inspection and basic form to sign off and fairly cheap (>$100). Most fitting Stations will not let you do the work yourself (to a decent standard) and then inspect and certify it - most will only certify if they do the work themselves (in the end it's their signature on the line). It pays to check with the one you have in mind before you fire up the drill and spanners to DIY. My FB sedan was "certified" this way and has the simple piece of paper to keep in the glovebox. This process was cheap (a hundred dollars or so compared to a few thousand for full engineering).
e) Some Fitting Stations require full compliance to ADR5 (
http://www.comlaw.gov.au/Details/F2009C ... 5628295870) when you install - there are some tricky bits in ADR/5 about how far apart the belts can be. Again, check with the Fitting Station you have in mind before flashing up the tools. I did an ADR/5 compliant system for my EK wagon. I took a full set of photos and measurements, and have turned it into a draft Guide. If you want a draft copy, let me know an email address.
I could be wrong with the above understanding of NSW legislation - happy to hear alternative views.
Cheers,
Harv