Got the second crutch strap mounted this evening, and slung the passenger seat in for work tomorrow.
Also had a good look at the sliders I've got to see how easily they will mount up to my sidemounts.
Answer is, Very easily! I'd rather not use sliders if I could avoid it, but one seating position just doesn't work for dad and I due to different heights.
The sliders I've got are Sparco double locking ones, so hopefully about as good as they get. will look at getting them mounted once I've finally got this cage finished!
I think getting in and out is going to be rather tricky :S