Replying to Fix My Ski Rack!

Sooo I go to put my ski rack on my car and the 4 bolts on the racks are completely rusted so that they won't loosen or tighten so I'm like fuckkkkkkk.  I went out and bought some stuff similiar to WD-40 that claims to loosen rusted parts etc.. and it worked on two of the bolts but there's still two left that it won't do shit to. 

I figure the best way to fix it is to find similiar bolts and cut off the existing rusted ones and replace them altogether but before I go and spend any more money on it does anyone else have any tricks to free rusted bolts?