Sorry to hear about your bad luck.
I am just in the process of setting up this same system: after cooler W/fan plus water separator; and then copper pipe network with gate valve drains. I bought the Derale brand after seeing it mentioned here by others.
Do you think its vibration causing them to fail? Can you upload a picture of the point of failure so I can try to remedy in advance?
I also have a separator just after the tank, and at the table I have another filter and a desiccant bead canister.
