Since the main wheels don't steer, you don't need to introduce camber or even caster. About 1 degree of toe in (total) should be okay. Nose wheels and tailwheels do need a little caster to remain tracking straight ahead. Caster dictates that the wheel involved wants to roll straight ahead instead of wanting to swivel. You want the axle to be well behind the centerline of the gear strut. But again that's only on the wheels that actually are steerable. Some taildraggers, and some light private aircraft will appear to have a little positive camber in the air, but on the ground with the gear loaded, vertical is what you want. Look at a full scale cub flying. The gear is unloaded, and the wheels appear to tuck in at the bottom, while on the ground, they are straight up. The main thing is not to allow the tailwheel to have too much authority (movement). A little goes a long way.

Bill, AMA 4720
WACO Brotherhood #1