I've done exactly the same thing for my canopy, because we'll be running a car fridge as a freezer in there, so it will generate a fair bit of heat, but went one step further. In order to help keep dust out, as well as cool it, I've also added a voltage switch, which is set so that the fan will come on while we're driving or when we have sufficient solar charging. The rest of the time the temperature switch, much the same as yours, takes over.
Just a note of warning if you want to do the same; I originally just wired them in parallel but the temperature switch was destroyed when the voltage switch activated, despite both appearing to use a relay in the output. To avoid that issue I simply placed a 1 amp diode in the output line of each switch, which isolates them from each other. Now they work together quite happily.