Chassis grounding for multiple daisy-chained units
There are many options to deal with chassis and GND. Here is what i do:


Power is always supported by two wires (power and return). 
Local ground may be connected to power return or isolated.
If local ground is connected to the power return, it can't be connected to any other ground, because in such case current has more paths to return.
Chassis is connected to zero potential (the one that is safe to touch) in only one point in the system. 
All digital and analog grounds (in contrast to power ground) are bypassed to chassis with 1nF and 1uF capacitors. If the GND is also considered zero potential, capacitor's voltage rating may be 50V.
Cable shields are connected with low impedance to chassis. With RJ45 it's easy, in DType or other connectors you have to make sure impedance is actually low- don't connect shield to wire to case, but rather find a place to make a wide contact.
Use filters on signals. Single-ended signals with single ended filters, differential- with common mode filters. 
Power and GND should always be bypassed to chassis (1nF and 1uF), unless it's AC voltage input (then just 1nF on each line).
Good luck :)