yateskid,
Don't forget: Supco Rust Buster (or something similar) is your friend in these situations. (I have no affiliation with this particular product.) Soak rusty nuts/bolts with it and then allow some time (a half-hour isn't excessive) to soak in before trying more torque. What's on the outside may have evaporated, but it's what creeps inside that counts!
I've used Rust Buster for almost 30 years. It really helps, especially with dry hard rust that's keeping nuts and bolts together - just like the kind you find underneath vehicle bodies.
You can buy Rust Buster from Amazon, but then, you can also buy it elsewhere for half the price. Just search for "Supco Rust Buster".
As an aside, musicians who play valved brass instruments like trumpets, cornets, french horns, baritone horns, and the like will instantly recognize the smell of Rust Buster. It's called "valve oil" in their world, and it can be found under that name at any musical instrument store.
Don't sniff Rust Buster (principal chemical name: glycol ether). When I was a young trumpet player, they told me it causes dain bramage - but I've never noticed any such effects . . .
Good luck, and may your nuts always bust loose freely!
Timerider