Mount the resistor in the air stream from the fan. A piece of Bakelite or other phenolic plastic works as an insulator/mounting fixture, and a small rectangular slot cut into the ductwork puts the resistor out of reach and into the moving air stream. The heat it generates adds a degree or two to the output of the heater, also. It's the way OEM blower speed control resistors have been mounted for at least 40 years.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!