From your description, it sounds like you know what and where the Univolt is located.
1. Can you hear the Univolt humming?
2. Do you have 120 volt AC power to the coach?
3. Are the circuit breakers in the 120 volt panel in the coach turned on?
4. The fuse block in most Univolt panels are labelled as to where to connect both the house battery and the charge line from the TV. As well as the negative (ground/common) side of the house battery.
5. Make sure the fuses, especially the large ones are good and tight in the fuse holders.
6. There may be a fuse in the negative wiring from the battery. This fuse is generally mounted on the inside skin of the coach. Somewhere close to the battery box.
The larger glass fuses are at least 30 amp.
7.Do you know how to use a VOM?
8.If the refer and water heater are original. They do not require 12 volt
9. The refer would require 120 volt AC power to run in the electric mode.
10. Do you have propane in the tanks and have at least one of the valves open one a propane tank. There may be a selector on the regulator to manually select which tank you want to use. Look for an arrow on the dial.
11. There should be shut off valves for all propane appliances under the coach. The handle need to be inline with the propane line to be in the open position.
12. It takes a long time to bleed the air out of the lines to the water heater and refer. Since the WH needs the pilot lit to open the gas valve. And the refer has a very small burner.
Answer the questions and ask more questions. There are many qualified people here to help you thru the problems.