In Australia, the  rear seats have to have shoulder harnesses per regulation. 

 

I ordered a full set of belts and harnesses for the front seats but without inertial reels, and installed them the back.  I anchored the shoulder harnesses to the top outboard area of the  main wheel well covers after reinforcing with a lot of carbon fabric (both sides) that I ran down the top of the wheel covers to the fuselage side wall and also down the bulkhead at back.  This is to carry the loads into the primary structure since the wheel well alone is thin fibreglass and structurally inadequate for the task of supporting the shoulder harnesses of rear seat passengers.

 

Fred