The Keenovo instructions recommend that you seal the edges of the bed heater with high temperature, red silicone RTV/gasket adhesive. Make sure you get it on, under, and around the wires. Seal that edge completely. This helps prevent the heater from coming loose later on. It seals the edges so that it is a lot ikely to get a bubble in the center over time.
Even better: put an adhesive insulation pad over the whole underside of the bed!