If you're real industrious there's a monitor system called the Integrity Tank Monitor System (about 170-200 depending on where you shop). It uses sensors mounted to the outside of the tank so the contents don't seem to affect it. I haven't personally used this, though I've been looking at adding it to my camper as I also hate the fact that my monitor never gives me good information.
As a side note, it can also monitor your propane bottles, though I think you have to get extra sensors for that, but is nice to have instead of having to go look and see if the flag is up on the changeover valve.
Those miracle probes sound good in theory kinda like this system.
Nights camped in 2010: 39
Nights camped in 2009: 31
2008 Ram MegaCab Hemi
Reese Dual-Cam WD Hitch
2009 Surveyor 304