To get the water in and out of the RF deck, I used a couple of brass fittings from the hardware store, and made a keeper out of a piece of aluminum bar stock.
I drilled a couple of holes large enough for the connector shaft to pass through, but small enough to stop the shoulder in the center of the fitting. The two mounting holes are drilled and tapped 8-32.
The chassis is then drilled with the appropriate holes to pass the connector shafts and mounting screws. Sandwich the shoulder of the fittings between the keeper and the rear panel, and there you go.
Short lengths of plastic tubing make the jump from the water jacket on the tube to the connectors.
One thing worthy of mention is that this brass-to-chassis connection serves another very useful purpose...safety. Any current leakage from the plate to the water will be shunted to the chassis here, showing up on the screen meter as reverse screen current. It will be most visible as a small meter deflection during standby. As the water ages, it will tend to conduct a bit, and the meter will thus indicate to you when it is time to change it.