Those fishplates are a good idea. I think I'll steal that from you.
Is there a big risk of warp/flex when burning these in? It seems like the 1/4 wall tube would be pretty resistant to that.
I cant quite see from your pics; where did you end the tube at the front? Are you into the Z'd area? I'd like to tie my 12' tube right into the Z with as few joints as possible...Less joints: less movement.