I'm a little over cautious on the safety but I have seen pictures of several of these truck mounted units on their sides. I operate cranes a good deal of the time and it is one easy machine to forget how fast bad things can happen. As far as the cribbing, you can get by with some 4' long pieces of rough cut 2x8 or 2x10 oak. If you want to get fancy make some cable loops on them so you can suck them out of the mud and even move them with the crane itself.
One last thing I forgot to mention, proper digging with the drag bucket also involves not dragging all the material to the machine if you can help it, once the bucket is full get it up in the air rather than drag more material to your "feet" so to speak, this way you don't have a pile of material drawn tight to you that you can't remove without moving the rig. You will have fun, you will work hard, and you will save money digging yourself.
Every man should own a dump truck.....heh heh.
