To construct it I:
Cut backrest and square seat, of each from the fabric, ripstop nylon, wadding and 2 types of padded interfacing; one super stiff and one fluffy (trying to recreate some stuff called Timtex which has been discontinued here). (You only need .3 of a meter for each layer)
Then for the backrest part I layered the Fabric with the right side facing the Nylon and stacked that on top of the interfacing's & wadding and over-locked 3 sides.
I used the open edge to turn the fabric right side out (over the padding so it looks like the finished product), then repeated this for the seat part.Then I over-locked the 2 parts (backrest & seat) together by pinning the fabric (right sides together), wadding and interfacing together and stitching (leaving the nylon free) on the open end and then hand stitched together the nylon to make a smooth seam on the back. I pretty much stuck to the measurements I posted last time, but I did end up shortening the seat a little.
Finally I used my sewing machine to add the button holes for the straps, the slits each all have to be at least 3cm wide to fit the buckles through (found that out the hard way). I measured up the heights as I went so it sat flat, for the backrest the depths were all 1.5" from the edge, and 1.5" wide. The center hole on the seat is 2" wide and completely centered. And that was it, hope that helps!
(Sorry for the imperial measurements, the pram seems to conform more to imperial than metric, which is weird for a NZ pram.. they are metric aren't they?)
Now I have to get myself in gear and make the weekender up as a nappy bag in the matching fabric!