I'm not sure the one that was a base will let you run it as a vehicle w/out receiving RTK again? 

So yes, you can do your plan with one of them and it lasts 14 days of SF3 essentially. But that second one you're using as the base for tiling....not sure if that one will go into RTK-X once you disconnect and move to a machine and change from base to vehicle. Have to try it and see I guess