Propane is stored and delivered as a liquid, but used by your heater as a vapor. The liquid propane volume in any LP Gas container is directly related to its temperature. Propane volume rises as temperature rises and falls as temperature falls. 60 degrees fahrenheit is your reference point. Propane users can become quite confused during periods of cold weather because their propane tank gauge may read less than what they expect it to read.
As to troubleshooting, the manual will have troubleshooting and maintenance procedures, and you can find those procedures on youtube videos. It is valuable to learn the furnace sequence of operation. I'm an advocate of RV owners expanding their service skills properly, rather than applying "try this or that" procedures.
One good water heater reference (yes the thread is re: furnace, but same advice), is at Atwood Water Heater Troubleshooting
Some of your basic tools you will need are a manometer, multi-meter, and circuit board tester, plus some common hand tools.
If you make it a point to perform maintenance twice a year, you can become more familiar with your water heater and keep the components in great shape. Water heaters tend to be out of sight and therefore out of mind. Get in a habit of opening your access door and keeping and eye out for rust, insect nests, and other visually problematic issues.
If you have a Suburban then you need to inspect the anode rode twice a year and replace it well before it is completely used up as it is protecting the inside of the tank from rust.