I agree that DSLR's are durable, there is a wide range of durability. For purposes here the D40/50/60/70 with their plastic bodies, and mounts, as well as being unsealed don't qualify as durable. This is not a slam on these excellent cameras. It's just that they are what they are, and F5s they are not. Drop one and they are, most likely, done.
Protecting the camera in foam padding in a waterproof container/bag should give plenty of protection. Give it the same protection you would give a laptop or netbook while traveling by bike and it should be fine.