Fuel gauge problem in a 2002 Holiday Rambler pusher

Fuel gauge became inaccurate and then stopped working all together. I was told that since it did not have a mechanical float the problem might be some kind of fuel contamination and to use a diesel fuel conditioner. I did and it worked well on the first 1,000 miles of a 4,000 mile trip. After that additional conditioner had no effect. Anyone have a cure?