It is no wider than the normal car seat but you are restricted as to where you can place the car seat by the isofix points in the car. It therefore means you can not bunch the seats up together which is not recommended anyway. What car are you trying to fit them in?
To be honest I don't really see the advantage of the base over strapping the seat in everytime if it isn't for the isofix. I think you need to go to Halfords and get them to try the seats in the back for you.
have to agree- the easybase is a sanity saver- also it is safer as it takes away the danger of the seat not being strapped in correctly- easy to get it wrong when you've had no sleep! nearly 40% of car seats are incorrectly fitted according to which.
The base didn't add any width to our maxi cosis- we could still fit two cabrios and a rodi in the back of a megane!!