SNS and I agree. He has found the text to confirm what I have done for 25 years. Basic physics and operational requirements or given conditions, don't really change to suit the operator's convenience. You just gotta do it right!
I need add very little to SNS through disseratation. I have used the "100W Mechanic's light" with success under the limited conditions of: a; no alternative, and b; right after shut down to keep the engine warm (not get it warm), and c; with a fitted insulated engine blanket. This means is still quite risky from a fire prespective though, and a last resort.
It is known to carry a small generator in the plane for overnight trips, so it can be run to energize heaters hours preflight.
For all the other care we take, let's get this right too!