Thanks H2J, yes, that sounds like a plausible solution. My thinking hadn't progressed past using the original rawl nut fixing system.
I would need to make sure the top of the nut doesn't sit too proud and stop the A panel from locating properly. I'd also need to get glue inside the sill to maximise the contact surface area, which again would be possible if access to the inside is available. Surely people who've checked their front jack mounting point could tell me if there is clearance to reach into the sill.
Another thought, would a riv nut do the trick? www.rivtec.com.au/threaded-inserts-rivet-nuts
I guess my main concern would be cracking the already stressed fiber glass when clamping the rivnut, or I simply epoxy one of these in place? I already have a non sag construction grade epoxy which would be perfect for the job.
Your suggestion has opened up a new path of thinking for me which is just what I needed, thanks.
Knowledge is realizing that the street is one-way, wisdom is looking both directions anyway