Or you can go this route and skip the spa-supplied heating element:

Inflatable Hot Tub Heating Hack:

https://youtu.be/Cr-q0NjwWRA

Link to the “bucket” heater:

https://www.amazon.com/dp/B07SYP8X8Q/ref=cm_sw_r_cp_apa_glt_fabc_1K82ZT54YWVH05YC8SYM?_encoding=UTF8&psc=1