The pressure of an open loop and the pressure changes are very minimal and not really a concern, don't overthink that part, esp trying to incorporate some kind of overflow system into a drip pan, this is def not needed. If you want, just get one of these or one of these and place it in an empty G1/4 port at the top of your reservoir. Just make sure you have enough radiator. You can save money by not buying a D5 or DDC, but then again you get what you pay for. EK has some info on radiator thicknesses.