Haha! That will be the big dog flap.
I'm building my reverse trike in the basement of my house.
Everything has to be be able to be taken apart and up the stairs and through the house for reassembly outside.
I built my electric tractor that way. Once built I took it apart for painting and then took the dried parts out into the trailer. When it was all there I rebuilt it all again.
There is a thread
here on Tractorbynet.
Just in the process of changing the broken transaxle on it now.