The main frame is complete!  After a 3 hour session of careful positioning and welding it's finally assembled, which means I can concentrate on getting the base done - then I might be getting somewhere.  As per usual with any sort of welding, I managed to burn myself (it stays hot for so long!) but this time I managed to melt a hole in it.  I suppose there's a first time for everything!  I also managed to use almost every tool in the workshop, which I'm quite impressed with.