Looking for user comment : Oil Sump Heater

If anyone has experience with the Reiff's HotStrip Oil Sump Heater,
will appreciate any input as to its usefulness/performance. 
Specifically, I wonder how well (how fast) this pair of 100W heater
strips can warm up a cold-soaked sump (8-qts) in an O-300 (open
hangar, assume low in the 20s overnight).
Plan is to rig it with a thermostat and an outdoor timer to have it
maintain a certain sump temperature, but figure that the ultimate
worst scenario will be to heat up from the 20s.  Plane is in an open T
hangar.

Thanks in advance

Javier Gorordo
c/o N1190F
08C, MI