i am glad you have raised this phil as i need to do the same to accomadate my 3 year old.i have a pair of new static belts from omicron which i have used in the front to secure a baby seat which i would like to now install in the rear.My s3 fulvia coupe had 2 factory mounting points at the rear of the seat base.i cant remember if there was a third.i can only imagine using the boot floor for this in a sport as i am not sure about the strength of the rear backrest crossmember.i do remember from installing racing 3 point harnesses that the lapbelt is straightforward but the belt angle of 'shoulder to mounting point' must not be too accute to avoid compressing the shoulders and spine?in a forward impact situation.also correct sized load spreading threaded plates should be used [behind sound metal reinforced if necessary]these are available from harness suppliers individually and have the correct thread.i would also appreciate advice on this subject to get it right first time as i would never underestimate the forces involved in a collision. richard