How silly can you get? I completely forgot that I took some pics of this triangle as I was doing it, so here they are. As you can see from my diagram, I added a couple of little seams in the middle. (I must have known this one wouldn't be particularly easy). I am sure there are some other ways of doing that middle section without the extra seams, but I couldn't think of any at the time.
Drat, I can't turn the pic around, sorry
[ATTACH=CONFIG]12452[/ATTACH]
Watch the numbers to paper piece
[ATTACH=CONFIG]12453[/ATTACH]
The centre section finished - phew!
[ATTACH=CONFIG]12454[/ATTACH]
Getting the triangle in
[ATTACH=CONFIG]12542[/ATTACH]
I hope these help
[ATTACH=CONFIG]12613[/ATTACH]