Help with rack

Planning to build a rack system using 41 QT long rubbermaid tubs. What size flexwatt should I use???

11" for the back, will do just fine!:D

Belly heat is the best, i use a foot of 11 inch on each 41 quart tub on my rack.

my flexwatt is located underneath the tubs to provide belly heat.

i use 11" because it creates a bigger surface area hot spot.

i also use a space heater to create the proper ambient temps needed for balls.