Well, turns out the "annoying setbacks" from yesterday were actually very minor in the end. Sure it meant more work today, but it was easily rectified. I also stumbled upon a solution for holding the lighting rig and backscene in place without having to bolt it to the layout.
On the temporary legs the layout is sat on (from an N gauge project many years ago!), I noticed a metal L bracket and realised that it was the answer. Unfortunately it was a bit too short, but I realised I could just saw a notch into the lighting support. The assembly is shown below and should be self explanatory. It means I don't have to bolt and unbolt the whole set up making it easy to assemble/disassemble by myself. Everything just slots into place, no screwing in or putting on bolts needed (unlike my other layouts!).
With everything attached, this is how it all looks. It could be neater (my woodwork is not great it has to be said), but I'm happy enough with the result.
And finally for now, the photo that I promised yesterday. You can see how the softwood battens help keep the backscene in place without the need for any fixings. The hole on the left of the lighting rig support will be hidden by a small bit of dune, the scenic exit being hidden by foliage and trees. The softwood block on the left had to be removed and the polystyrene trimmed so that I could fit the lighting rig in (as mentioned yesterday). It's finally coming together now!