I would be very leery of using any portable propane heater in the shop.  We almost lost a good friend last winter to carbon monoxide poisoning.  He was working on a piece of equipment in his shop with the door open with the heater in the doorway.  He didn't realize the wind was blowing the CO into the shop.   He survived but has suffered some neurological damage and can't go back to his old job.  He's also farmer and now needs help on some of what he used to do around the farm.