Thanks Vilguy. I appreciate that. I hurt my back a few months ago, so I'm trying to do as little heavy lifting as possible, so I'm aiming to simply copy what you've done as much as possible rather than reinventing the wheel.
What confused me was when I had a quick look at the seat, it looks like the existing smartcar ones have a bolt hole at the front on the vertical, rather than horizontal! They are at the back of the garage though, so I don't fancy getting them out to have another look. Seemed much more comfortable than my defender ones though.