Cut the head off of that bolt with that grinder....put a cut off wheel on it...then you can remove the rest of the bolt when you have already removed the bed and you have better access to it.
Cut the head with a cut off wheel. Cut it once, turn the.grinder 90° and.cut.again. Repeat until youve.got 8 triangles left. Like cutting a pizza. Take a 2lb hammer and cold.chisel and bust that head off. If you do.it as.described you wont much up the paint.