Had a single $30 stick on pad from Amazon that would heat my 540 all the way to the rocker covers overnight. There are hundreds of shapes and power levels available - no need to look at any of the "aviation specific" models, IMHO.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
PA-20-inspired "family truckster" -in work