I got the beads on Amazon (
https://www.amazon.co.uk/gp/product/B01N6X7DKM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 )
£5.99 for a pack of ten.
I placed one right next to the front cam which is visible , and then concealed one very near this behind the rear view mirror trim.
the two next to rear can are about 10cm away from the rear cam and behind a trim panel, then the two for luck i put on the excess cable behind a trim panel.
I have seen some comments from others that ran cable on the floor, but i went the head liner route. Maybe try a temp (tape or cable tie) on each side as it may narrow down the best route for you, before you tuck it all away neatly. Also maybe try rear cam at top and bottom of rear screen as this may make a difference as well? I went for top as seemed most obvious place for best view, but you do notice it in the rear view mirror to start with.
Worst case the Ferrite beads did work for me, so may be OK for you.
Paul, what diameter ferrite’s did you use as they are only showing 3mm, 7mm & 9mm?