Thanks for that idea rsxe240...I watched them make enough of those speaker boxes on Discovery and never even thought about going down that route. As you say the reduction of buck size would be an issue as I'd rather have accurate external sections to work to. I guess if you had external profile guages to lay over the work to check it it would work but then you also lose the datum points as to where the profiles should be on the body. I've kept the outer profiles when I cut my templates out just incase things go horribly wrong!
A quick update. I've starting closing off the box sections which didn't take too long - just stuck some balsa strips in place around 7mm below the surface. More sheeting was added on top of that:
When dry, I attacked it with the Dremel! My aim is to give the bondo something to key onto and to weaken the balsa edges. Hopefully this will make the final removal of the balsa surfaces easier and allows the bondo strength to pass through the wood giving it some structural continuity?
I've also painted the edges with black enamel so that they show when the filler goes on. Not sure if the filler will attack it yet but about to find out!
Given the size of this thing I'll probably tackle it in 8 separate sections so that it's not too daunting a job, eg. front, back, the two sides and four wheelarches.
Darren, meant to add that I remember Fibre Fab very well (and their rare Alfa conversion) Used Fiesta headlights IIRC?!