Got a lot completed today, all the internal structures supporting the seats and the controls are installed and tack welded, also the windscreen diagonals are installed and tacked and I'm about halfway through installing the support structure overhead the main cabin. Once this is finished then the fuselage main structure is ready for final welding. Based on the experience with the fuselage sides, I estimate it will take about 24-36 hours of solid work to complete the welding and a lot of Argon! I hadn't appreciated before starting the build that Argon is going to be a significant cost (c£500) whereas it looks like I'll only use about 3kg of filler rod (£25).