Hi 5catfam,
The underbelly being heated from the furnace is standard. Heating pads on the holding tanks used to be an option. Now I think it may be a "special order" option. When so equipped, there will be a wall switch that looks like a residential light switch. Maybe with a lighted red switch handle. It's usually located with all your other special trailer switches and tank monitor panel. Usually they are marked (Tank Heater?). Mine switch was not marked so I added a label.
Perhaps someone with a BH 3055 that has the option can reply with a pic??
In 3 years, I never used my heating pads.
Jim
Picture from my 2005 Landmark: