If he is open mouthed breathing, it is a very large sign of a respiratory infection, rather than the shed. Though the shed could effect the whistling.
raise the heat to low 90s!
not too much, we arnt trying to kill the little fella haha.
This should be fine till monday, just watch him close, and keep us updated.
(oh and before i forget)
if its too hot, he might not leave the bowl. The water will keep him cool, and many snakes soak when in shed.
i hope someone chimes in to give better advice, these are just the basics.