Really weird power issue

You have a bad ground somewhere.
The power is back feeding through said 30A fuse.

What does the 30 amp fuse power? I am guessing it is the battery circuit and the battery is shorted out.

I missed that part. The battery isn't on the trailer. Simply shore power.

If the 30 amp fuse is actually a breaker and your battery positive cable is lying around shorted to ground your converter/charger is trying to charge the missing battery but is instead feeding that power to the shorted positive cable.

The breaker is probably cycling on and off enough to get hot. A fuse would burn open IF the short is a solid low resistance short but if the short is not making a good contact it could allow almost enough current to blow a fuse.

Pulling the fuse removed the short so to speak and allowed power to get to the other circuits.

There may not be enough power from your converter alone to run an awning or heavy current item. Your converter could be a real wimp and just big enough to charge the battery but not big enough to run any big loads.

The 30 amp fuse/breaker could be misleading however correct in that it is just that size to allow the battery to supply that much current FROM the battery and not sized for the charging ability.

That is probably not clear but in any case you will find the short on that positive cable somewhere.

Yes, isolate the battery cable as suggested by YC 1.
Or if it is the bat fuse, leave it out. Verify that your converter can operate properly without a battery.

Thanks everyone. This turned out to be a case of me forgetting something simple. You were all right. I was grounding out badly. When I put the trailer in storage, I put the battery cables through the propane tank retention screw to keep them from dragging. Pulled them back to their proper spot, and problem solved! Simple fix, but it almost drove me to drink last night. Thanks again!

Thanks for the update!
Now you can have a good drink! Maybe have another one!

It's 8 am here. I will wait an hour or two. ;)

If you have to look at your watch to see if you need a drink, you don't need one! Bloody Mary?

Wouldn't hurt to put some tape on those cable ends to prevent future issues!