This is the model I will probably use: http://www.rvgauge.com/products/model_7094.shtml
The SeeLevel line of monitors uses a different system to determine liquid level. Instead of physical contacts in the tank (which get covered in goo, and causes them not to sense levels properly), the SeeLevel system uses electronic magic and senses level through the tank, and remain accurate. We boondock a bit, and knowing the remaining gray water capacity is nice.
You have to attach an electronic circuit strip to the outside of the tank, and then use the old wiring to connect the sensors to the display panel. So, I have to figure out how to get access to the tanks. (At the moment, difficult for me to do, since the trailer is still in Indiana being built.)
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch