i don't have any experience with heat cable so i wish i could help. does heat cable work for ambient temps?

last winter i got a 100W CHE for my 20gal and it's worked well. do you not want to use lamps? i can understand if you don't; they're not ideal.

not too long ago i was actually looking for a way to heat the cool side of my 15qt tub i have. do you have any experience with plastic tubs and heat cable? just curious.