If they have been on there a while, you may need to tap on it around where the nuts came off. That is what worked for me the first time I did it. No special trick to get them off. Probably just some corrosion in the threads holding it captive.
Your bus looks just like mine. Nice condition if that's a recent picture. How are the tan decals holding up? mine are shrinking. Other colors are in great condition. Think there was a bad run of tan decals back in 2004.
The passenger side decals are great, drivers side has sun damage. Have a man coming tomorrow for price of the blue decal. It is a local sign guy he does decals for local rv dealer and county vehicles. He has to take photos and measure.
I would be very interested in the cost of re-striping a section.
Did you ever get the wheel liners off?
Have you looked for windshield frame rust yet? Had the trim off mine a couple years ago and cleaned up where the rust was starting. Will be re-inspecting again in the spring.