It looks very nice! When you add a gusset here and there, it will be stronger. Don't think the tail would need it (though personally I would add it), but the motor, I definitely don't feel comfortable about it being mounted like that. It could use a bit of reinforcement, I think.
Will be building my own mount soon too. Will be made out of stainless steel though. I know it's a bit more expensive (not where I shop, the scrap dealer ), tougher to work with and has lower strength.
However, the corrosion resistance (and thus, need for maintenance) would be reason for me to go that route.
I'm surprized that I've never before seen pictures (as far as I can remember) where some built his mount out of stainless steel (apart from Joe WXYZSCIENCE's downwind turbine, which is partly made out of SS, but has a quite different design from the standard furling mechanisms).
Peter.