Need help keeping a rigid mechanism in a 60ºC(140ºF) Incubator

I've built an incubator with an electrode at the center with the purpose of cell culture, screwing a block with copper tape at each of the ends of the electrode to pass current, but given the fact I need the incubator to have a temperature of 60ºC the nuts and bolts come flying out when I reach that temperature. How would you prevent it? adding weight to the blocks? changing the types of bolts? or what would you change in the design? Here is an very rough schematic of what I'm talking about. (http://imgur.com/HkY7kSS)
Any help is greatly appreciated

What kind of bolts come apart at only 60C? What are they made of? Wax? I'm not sure I understand your description of things.

Not sure that I understand, either. If thermal cycling is making your fasteners come loose, you could look into locking nuts. Nylon locking nuts ("Nyloc") should be fine at 60deg, but there are all-metal locknuts available for higher temperatures.
60 degrees is barely warm, though, so I would be very surprised if thermal cycling was your problem. Is there a material involved that's getting soft at 60 degrees - maybe a plastic of some kind?