When we had our 3400, the tank gauges (water, sewer, propane) worked for a few trips then quit. Our MH has a Sensa Tank Level Guard system. It is not cheap, but has worked perfectly for two and a half years. We have two units, one in the outside water compartment and one inside the cabinet where all the AC/DC controls are located.
http://levelguardproducts.com/marine...nk-monitor.php