Thanks - I did call the folks at Rieco Titan (who made the jacks) and they advised that all 4 jacks should be able to be used at once in this camper. I haven't added up the loads though - this wouldn't explain the power drops when the jacks aren't in use.
However, I was just out with a meter trying to troubleshoot. Does anybody know what this thing is?

I noticed there was power to the right side, but not to the left. When I wiggle it, battery power comes back on briefly - but it won't stay on. The connections are tight, so that's not it.