After burning up an SSR (which leaves the bed in an always on state) I switched to the TriGorilla Mosfet heat controller to relay power to my 280w heated bed (https://www.amazon.com/TriGorilla-Printer-Heating-Controller-Extruder/dp/B01HCVJ3K2). This device is pretty great and stays cool to the touch even after heating the bed to 100C. It does require more connections and just leaving it open on the floor of my FT-5 didn't seem like a good idea.
I created this case to accommodate the wire connections as well as leave plenty of room for a fan an ventilation. You will need four 12mm m3 bolts and nuts. I used 3m mounting tape to secure it to the electronics box.
Print the bottom without supports to keep the nut captures clean. Top needs supports to print.