Fitting infant car seat

Hi,
Wondering is anyone can give me some advice please. We have bought a Safe & Sound Meridian AHR to fit into our Subaru Liberty. The problem is that we live in the Northern Territory and there is no qualified person/company in town that can help fit the seat, so we are going to have to fit it ourselves. We have the seat in place in the middle seat where it fits and due to the slope in the rear seat a towel is needed underneath to fill the space. Once tightened and in place I have found that the car seat moves alot from side to side when it's in the baby mode of full recline. Any hints or tips to what might be wrong I'd be most grateful.
Thanks
Carol

if u have a retractable seatbelt in the middle u will need a locking clip.

Some small movement is normal. It will tell u this in your book. It has something to do with if the car crashes etc... cant think off the top of my head...

Thanks for the reply, What do you mean by a locking clip? Different from the anchor point on the roof I presume. I know there should be some movement but it seems to more than just slight movement. I have noticed that if the seat isn't on full recline, the seat locks secure and doesn't move as much but realise for our new bub we need it in recline.

check out this site - Locking Clips

Car seats do tend to move around a lot when not professionally fitted. Do you have the stabilising bar extended?

you need a "H" clip i call it and it turns your retractable seat belt into a lapsash style seat belt so it cant move it is fixed at one length. this si then put through the base of the car seat and if you sit / kneel on the sit fit the seat belt so it is sooo tight you can only just get the clip in, you will have minimal movement.
this si how the lady who installed DD's car seat showed me as we were moving the car seat from car to car regularly for a few months.