I am in the process of installing a Heater Craft three outlet heater in my boat so I thought I would post up some progress pics. I bought the complete kit including three extendable heater tubes from go2marine.com for $396 + shipping. Many thanks to csmsk (Chris) whose detailed install post inspired me to tackle this project.

Most installs I have seen that incorporate shutoff valves have a short length of hose between the engine and the shut off valve. The obvious issue here is if that hose leaks, the shut off valve won't do any good since the hose is before the valve. So I decided to install a series of brass fittings (all from Home Depot and Lowes) from the block to the shut off valve, both at the supply and the return. This way, if I get a leak anywhere in the hose, I just shut off both valves and I'm good. I can finish out the day and fix it when I get home. Below are the pics:

This is the supply line. There used to be just an allen head plug here. I used pipe joint compound at all the threaded joints.

This is the return line. It's tight but it clears the recirc pump hose. There used to be just a square head plug here.

This is the heater core mounted on the front of the footbox and electrical wiring wired to a spare switch on the dash. You can see the 2" hole on the left thru which the heater hose will be routed. I drilled the hole fairly high so that if I take a bunch of water over the bow, hopefully, it won't make it into the footbox. I can't come up thru the existing hole in the top of the footbox because when my sub enclosure is in place, there is no room for the two hoses. It was a royal pain to install this heater core because of the cramped space you have to work in.

That's as far as I've gotten. Will be removing the floor next and run the heater hoses from the engine to the core. Then the fun part - drilling three 4" diameter holes in the gelcoat for the heat tubes