If I remember correctly he used marine boat Hatch covers over the Mopeka sensors.
smartmarine Boat Hatch Black 4" 6" 8" Round Non Slip Inspection Hatch w/Detachable Cover for Marine Boat Yacht
https://a.co/d/dnFgSoh
I saw a video on YouTube where a guy installed them on a Class C. He cut three holes before he found the correct location to place one. One hole he cut was over the tank heater.
The forward drop down under the bathroom and Black tank is easy to take down/up. Start at thr back and work your way forward until you have enough down to work under the tanks. Of course you have to place it away from the tank heater.
Then push up the coroplast and mark where you want to install the Hatch.
To put the coroplast back up I supported it on leveling blocks and a long 2x4 to get the screws started. Use 1" #12 self drilling bolts through the nail holes you pulled out.