So let's see...
1) is very similar to Clam's solution. The same fix I made for that one should work there.
3) is hilariously awesome. I never expected that way or a variant of to be possible. Again, though, that doesn't seem that hard to fix.
4) is quite clever. I like solution 4 and might not bother to fix it.
Also the intended solution may be possible with 1 digger if a floater is used for the purpose of the other one (EDIT: 1 digger confirmed possible for intended solution) -- in that case I don't know if you can repeat 4 with a single digger, but I'd not be that surprised.
I'm just happy no "Let's Go Camping" style backroutes were possible. At, least, I don't think...
Thanks for showing me all those routes.