Dave,
Here's a pic of behing the firewall on mine.
The box was originally built just to enclose the back of the engine. I'm planning on glueing another piece of 3/8 lite ply to it. If I can then figure out a way to secure it to the sides of the fuse (as you can see, the way the interior of the fuse is designed, there's not much surface to glue traingle stock too like you normally would), then it should be easy enough to bolt a mount to it.
At least, that's the plan.
I see you're in Indiana. There's (what should be) a pretty good size WW1 fly-in schedule for Sept. 25th by the Hamiliton Co. club,
and our clubs warbird fly-in (all types) is coming up July 24th. Have a look at the [link=http://www.bealmear.com/dawn_patrol/2004_events.htm]RC Dawn Patrol, 2004 Events [/link] for more info.