I forgot to say I tried the shop light approach on my cessna which is in a hangar in the northeast.   That and a big sleeping bag and some plugs worked "okay".  Then I got a pan heater with a thermostat.   Way better.  heat goes where you want it when you need it.   Just leave it plugged in all the time and the airplane is always ready to start on the 2nd blade..  I'm thinking about a pre-oiler now...

Someone asked about just using thin oil.  It's not just the oil it's the relative dimensions of all the metal parts.