Please help with heat tape size

[Coleslaw007]

I am having a 41qt rack built very soon for my large females and I have gotten lots of contradictory recommendations on the size of heat tape to use. One person will tell me the 12" is what I want and the 4" is too small, another will say the exact opposite. So, in 41qt tubs, what would you guys recommend?

Thanks, guys!

Edit: Tubs will slide out longways, not sideways so the narrow part will be on the tape, not the entire length of the tub. *Thanks, Mike!