We have fust ordered a Cambee full width R&R bed with their easy fit kit for our LWB. Won't allow forward and back movement but does allow 'relatively' easy removal.
RIB was no good to us as it sits to high. Both of us being over 6'.
We haven't fitted it yet so can't comment on how it works in use but I liked the set back position of the one they had at their workshop.
We have a dog as well but use an elasticated cargo net between the front seats and a harness attached to the lash down point (highline kombi) feature we kept, whilst travelling. He happily lives on his bed behind the front seats.
Looked at the rails with the cambee and others but £2,500 plus loss of head height made us decide against it.
Not many rear passengers likely so distance seat is set back not an issue, infact with my lads being well over 6' as well they will love the legroom when they do need a lift.