I just went through this with my trailer.
You have an impact gun? I picked up an electric 1/2" from harbor freights for like $50, (worth it's weight in GOLD for this project) I was able to remove my nuts like normal, with the impact gun, then I sprayed it down with pb blaster, then, and here's the key....
put the impact gun on the bolt head (with no nut on the other side) and spin the crap out of it, forward, backward...etc. When it starts smoking, stop and spray it down with pblaster again. Then spin it some more. While it's still smoking hot beat the shit out of it with a heavy hammer, while swearing and cursing loudly at it (I used a splitting maul).
After that they came right out! :D
In most springs there is a nylon bushing, I'm thinking you've got to melt it a tad to get it to release from the bolt. At least that's my story!
1984 Ocean Yachts 38 Super Sport
Twin CAT 3208 355hp
SOLD::: Sea~Chelle 1998 246 Open Shamrock 350 TBI Inboard