You can buy cheap aluminum tape at home depot.
Truthfully I have used HD clear packaging tape for 2 years and have had zero issues.

I wouldn't use 3 or 4 inch tape on a 41 qt tub because of too small of a hot spot.

I use 3 inch for my 6qt tub melamine rack.
4 inch in my 28qt melamine rack and it is barley enough heat IMO and I still have to heat the room up so the cool end stays above 75 degrees.

11x12 inch for my 40qt tubs.