Are you asking about the heater box (or your board)? Just don't
use really long screws if it's the box over the heater core.
I'd probably find something to zip-tie it onto - rather than screws into
the heater system.
Not knowing what he really intends to do without seeing it doesn't help.
My gut reaction would be to mount it to the cowl intake box, directly
above the heater. Mounting it to the heater box means having to unwire
all that crap or leaving enough slack to move it out of the way if the
box has to come out. It's also subject to being kicked if he doesn't put
a cover over it.
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