Alan,
Very thorough job of engineering and fabrication! In the future, you might consider increasing your heat tape wattage to accomplish the VO heating, without the lamps. Many industrial sites use this technique to maintain fluids at elevated temperatures, so it is a proven technique.
I have installed primary and backup heat trace systems to allow for future failure and easy switch-over to the secondary system. Also a variable voltage control, such as a rotary motor speed control makes it easy to adjust for the need of additional heat.
Good luck with your alternative heating system! You set a good example of recycling the earth's resources.
Homer
