I have used the Duet in a 45 degres, and I have overheat warning on the TMC.
At 48 degres, the TMC shutdown, but the board was horizontal without ventilation.
So it could be ok if the board is cooled with fan on TMC and mosfet of the heatbed.
For the PSU, I have inside the enclosure a passive 500W 24V psu, but the dissipative face is cooled by watercooling, so the psu is at 30 degres.