Now, here is how to check for a draw:
1- Make sure the battery is fully charged to begin with, then unplug the main power.
2-Remove the negative battery terminal, and place a test light between the terminal, and the negative post of the battery. If there is a draw, the test light will light.
3-If the test light does not light, hook the umbilical to the tow vehicle, and retest, with the tow vehicle both running, and off.
4-With the test light lit, disconnect fuses one at a time until the light goes out. That circuit contains the draw. If you remove all the 20 amp fuses, and the test light is still lit, the problem is probably in the Univolt. Disconnect it from the system, and the light goes out, you have narrowed the problem to the Univolt, and can replace it.
5-If the test light remains lit, check for non-stock items that are wired directly to the battery, such as a radio amp, or TV antenna booster.
6-If the test light never comes on when performing this test, remove the battery and take it to be checked, it may have a problem that causes it to drain itself.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.