I used the following parts:

  1. Tempco 500W 120V heater
  2. generic 100K thermistor
  3. 24VDC fan - FCI DA-119B-W24 with ball bearings
  4. Crouzet GN84137180 250A 660VAC SSR - ridiculous overkill, but handy at the time
  5. Anderson power pole connectors
  6. lugs and wire
  7. 1" square aluminum tube
  8. a couple printed parts to hold things in place with zip ties.

It's all working fine, but I need to finish a couple things.  It needs a TCO to kill power in the event of an SSR or fan failure, and something to cover the electrical connections at the heater bar.  I also need to figure out a way to protect against the controller losing its mind - maybe a low temperature TCO in the enclosure that will cut main power if the enclosure gets too warm.