I now *think* that the second, two-stage regulator is bad. I already replaced the first, single stage one that regulates to 30 PSI and is easy to replace as it is just outside the tank.
Working underneath I found a second two-stage regulator. Confirmed this with Winnebago. This one regulates down to 11 inches WC (different from PSI). Fortunately, the distribution manifold downstream from this had an extra, plugged, port. I removed the plug and attached a gauge that I bought, and sure enough I have 11 inches IF nothing is running. As soon as you try to light the stove, it drops down to around 3 inches.
So currently I'm guessing it is the second regulator. I have one on order but it is a day ore two out.
From everything I've read online, having spare regulators in the camper is a good thing, they fail often.