I use a metal chassis that is 7 inches wide, 5 inches long, and 3 inches tall. This is the right size for four Radio Shack 276-150 PC boards inside the instrument and the LED displays on the front panel. I use two SO-239 connectors for connecting the directional coupler to the transmitter and receiver in order to be consistent with most transceivers. The back panel contains these two RF connections and a DC power connector. This DC power connector MUST be an insulated one so that the DC and RF grounds remain isolated. The front panel contains 22 holes of 1/4-inch diameter each. Ten of these holes are used for the SWR meter display, ten of these holes are used for the wattmeter display, one hole is used for the "idiot light" that indicates that a power supply has been connected, and one hole is used for a switch that connects the power supply to the circuit.
The rest of the circuit handles only DC, and stray inductances and capacitances are not a significant issue.
I dedicate one board to the LM324 operational amplifier, one board to the SWR meter display, and one board to the wattmeter display. If you use four Radio Shack 276-150 PC boards, I suggest putting the power supply connections (including the protection diode, capacitor, "idiot light" LED, and its current-limiting resistor) on the LM324 board, as the remaining two boards will be crowded with LED connections for the displays. Again, you MUST be aware of the dangers of polarized capacitors, and you may wish to substitute a nonpolarized capacitor or a series of nonpolarized capacitors in parallel for the 10-microfarad capacitance that only a polarized electrolytic or tantalum capacitor can provide.
The DC and RF grounds are connected by a jumper with four FB73-101 ferrite beads. One end is connected to the RF board, and the other end is connected to a DC board. The DC grounds on all three DC boards are connected with a jumper wire.