If the covers you're talking about are like mine and many others I've seen, there is a large T-handled deep well socket that came with the unit specifically to remove these nuts. They shouldn't be on very tight as they only hold the cover on, not the wheel. That being said, a week ago I had to fix a tire on a unit that came into our shop and I guess the last person to touch those nuts used air to tighten them down....NOT necessary. Have you looked to see if you have one of these sockets rat-holed away somewhere in your unit?