Would advise MOST strongly AGAINST having any hydrocarbon fuelled heater in a workshop.
1) Burning any liquid fuel, or gas will produce water vapour, and lead to rusting.
2) Leaving a combustion heater unattended HAS to be fraught with danger of fire.
A 80Watt "frost stat" tubular electric heater is about as much risk as I take with an unattended heater in my shop.
And you need ventilation, (You produce water vapour too, in your breath). A low level vent to let the heavy water vapour escape, and a high level one to admit replacement, and hopefully, drier air. Both need to be weatherproof, or it defeats the object. Ideally they should have a mesh to prevent all the local insects climbing in for a cosy home.
Rust, or the risk thereof will be greatly decreased by having the shop well insulated. It will prevent the rapid changes of temperature that promote condensation, and will make it less likely that your breath will condense when you start work, before the heater reaches your chosen temperature.
Howard