On Battery, lights ok; slide, awning & jack kill battery

Jack and slide motors pull a lot more 12v power than lights...
Sounds like a weak battery either not fully charged or is not being charged by the converter...is the converter supplying a charge to the batts? This is easy to check with a multi-meter.

There are a couple of blade fuses on a converter (mine has 3).

Good luck with you search of the infamous electric gremlin...