Both out kids seats seemed fine in the back of me 3 dr.
The youngest was bumping round in a Britax First Class - I think, he's now in one of them £25 ones that's always on offer in the soopermerkats, graco maybe??
OK, so there's a likkle bit of space between the side of the interior and his car seat, but that's the wheel arch and not really a lot I can do about it!!
To be honest we've often had 3 kids in the back seat - Tom in his £25 hacker seat, Em on some pink princess plastic thing and Em's mate on a Bubble Bum - blow up car seat - all have been safe and secure even on some mild laning fun where they absolutely got shaken around like beans in a can, but they all stayed belted in place.
Depends I think on the size of the kid, size/design of the seat itself and how they run the belt round it, as in the seat rather than the kid!
I presume you is talking about a seat for a tiny sproglet rather than an older one - some of the baby baby seats, need the belt almost a full stretch and out to the back of the drivers seat to get round the design.
