lots of guys on here will comment on their methods.
I searched far and wide, found that your idea is good...NAPA typically has Kat's pad heaters, decent price and wide variety of sizes and wattage. I tried some of the heavy truck & equipment places too, wolverine may have been the other brand..
http://www.fivestarmanufacturing.com/kat_s
https://www.wolverineheater.com/Articles.asp?ID=259
I only found one spot on the forward right side that I could glue the thing on without bridging an oil plug casting or some other darn thing! ..and try to get ALL the oil off that rough casting.....so the thing will stick!!!
I am parked outside, so needed the most watts per square inch I could find.
I also slapped a little pad onto a piece of aluminum, then sandwiched it against the side of my battery; figured that would give me a little more crank.
only tried it once, in a hangar of all things. It did warm up the sump in a few hours, and the engine started easily, no doubt getting better lubrication than a cold start.