I ran an i3 in a complete enclosure like that for quite a while with no issues with ramps/mega up to 45-50 deg C chamber temp. I don't know what the upper temp range is for Duetwifi processor & driver chip, I am sure David/Tony will chip in. But bear in mind that at 50 deg C ambient your hotend heatsink and electronics (and motors - but they can take it usually) can never be lower than 50 deg C, and will rise well above that 70-90 deg C wouldn't be unexpected. My Duetwifi which is under my mains powered (insulated) heated bed, runs at 45 deg C, CPU temp during printing, with ambient air being blown through the electronics case by two 50mm fans in push-pull configuration.
Consider bringing outside air into the enclosure for the electronics (and even the hot end heatsink + for part cooling if you go much above 50 deg) which will cool your chamber so it might be easier to move the electronics out of the enclosure. Sounds like hassle but its a £150 cock up if you cook it.