Temp control is one of the issues with both heat exchangers and certainly exhaust wrapping. This is a reason 12V heaters are a good choice. With your thermometers, you can control oil temps a little easier if it gets too high, just shut them off or install a thermostat like in a hot water heater, they're designed to work together anyway. Input your perfect temp to mix and the thermostat takes over. You could even mark the thermo for mix ratio's, this way you can find perfect settings on the fly.
On the heat exchangers, you can always install a flow limiter to control hot water circulation, I think one of those vacuum operated chingases that controls our heaters would work nicely, especially if it could be set up for mid-ranges as well as just off/on. Since some of you are using manual controls, same thing could be done for the flow limiters, simplest- just a cable controlled valve into the cab.... like one of these:
http://www.jegs.com/i/JEGS-Performance-Products/555/15830/10002/-1?parentProductId=762888
They can be used to shift fuel valves too. Daisy chaining a supply and return valve can double the duty of a single pull, or, if a rocker system is used, can control both tanks systems simultaneously. Of course, the more complex will require heavier cables to move all 4 valves at once in the fuel system. Five pulls mounted under dash might enhance the interior too. Red handles for front tank, blue handles for rear tank, green handle for water heater control, or all same color with labels.... you get the drift.
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