If you've got a battery disconnect switch (AKA Salesman Switch) check that first, it could simply be turned off. If it's turned on make sure that the power is actually getting through the solenoid that the switch controls.
If that's not it, there should be a main fuse mounted somewhere not far from the battery in the positive cable. Follow the cable from the battery, I wouldn't expect it to be more than a couple of feet from the battery, probably mounted to the nearest wall/bulkhead.
2013 Winnebago Sightseer 36V