Per CG5, last sentence, "For setup purposes RG must be able to trace a path (of any length) of contiguous, Enterable (by all units of that RG) friendly-Setup/Uncontrolled-Teritory Locations frommits Setup Area to their Eligible Entry Area. This path may not cross any non-Ford stream hexes." It is a bit hard to apply this to fortifications, as it has no units to determine whether a hex is enterable. I would suggest treating the RG as infantry. But it is clear that crossing a non-Ford stream (and presumably, stream-JD) hex is right out. My read is that until a ford has been created, the Americans can set up no purchased RG, including fortifications, south of the stream. That said, per SC1.4 Infantry may set up in foxholes, independent of RG purchases and of location, and without digging. As long as you set up a unit in a suitable location, you can put a foxhole there. I also play that in order to *add* foxholes to existing foxholes, the existing foxholes have to be insufficient to hold the units that want to set up entrenched in the location, i.e. if there is a one-squad foxhole in the location already, you can't set up a halfsquad in the hex to create a two- (or three-) squad foxhole.
JR