There are quite a few to choose from. What is your opinions on a complete system, from scratch. There is no system currently installed.
1996 Prevost RV Conversion
This is what I use for my Fuel Tank. Haven't run out of fuel since I installed it. ;D
https://www.amazon.com/Mopeka-Check-Universal-Sensor-Collar/dp/B0C7HM61BP/?th=1
This also works for fresh/grey/black water tanks too. You just need access underneath your tank to mount it.
I have the SeeLevel Tank Monitoring system.
I have been quite happy with it.
The best thing about this system is you do not have to make any holes in your tanks, just stick the sensors to the outside of the tanks.
I have had it in place since March 2021 and have had zero issues with it.
One of these days I need to remove the painters tape from the sensors I test fit them with and stick the sensors directly to the Tanks.
As an added bonus there is also a volt meter on the panel and I see the newest version has Bluetooth so you can check the tanks on your phone.
https://www.rvupgradestore.com/Garnett-Technologies-Model-709P3-SeeLeveL-II-p/709-P3.htm (https://www.rvupgradestore.com/Garnett-Technologies-Model-709P3-SeeLeveL-II-p/709-P3.htm)
Peter