Jim......when I had my 2005 Monaco, I added a sensor system, (forgot the brand name and the company later discontinued making the unit) that used the same strip type sensors. The system would read the water, battery and propane perfectly, but was finicky when reading black and grey. I called the company and they said they had issues with the sensors reading Monaco tanks due to their thickness. I never got them to read perfectly, but it helped when I placed some dense foam between the sensor and compartment wall, putting pressure on the sensor. It might be worth a try.
I loved that sensor unit because it had a digital display screen that showed all of the tanks at the same time in percentages, in increments of 5.......100, 95, 90, etc. It also showed the battery numbers too.