they can be a problem on rust belt jeeps, if your frame is rusty you might have a problem. one thing you can try is to drill a very small hole in the frame at each bolt, just big enough to get the straw on a pb plaster can in. spray them every day for about a week before you remove them.
if you snap one the best way is to weld a nut on, the heat from the weld will help to break it loose.
I put never seize on them when I re-assemble to make it easier the next time.