after i routed the channel i covered the exposed melamine with metal duct tape,to protect the melamine from humidity and spillage and the metal tape helps directs the heat upward.
once the metal tape is in place i spot glue the heat tape directly on the metal duct tape with silicone caulking.i've made racks this way over 7 years ago with no problems.btw the tub does not sit directly on the melamine (heat tape),there's a gap between heat tape and the tub.have fun!