Thanks all for the additional info and thoughts.
Tom, I liked those eBay boxes you posted the link for! I'll have to contact the guy, it looks like he may do fabrication for mounts on various bikes. Heckuva deal at $90 (a box I'm assuming).
Redhawk, thanks for the Caribou info, I'll look at their site too. I've seen them mentioned highly various places like ADVRider.
Andy, which model of HB box is that? XPlorer or something else? Those 40L look pretty good. Those and some handguards like barkbuster and I wouldn't even need engine guards. Do they hit the exhaust?