position lights

Hello everyone, please excuse me if this is a stupid question but I am very much a caravan virgin. I have a 2006 Ace Award tristar, the one with a fixed athwartships bed. I had to change an offside bulb and whilst removing the four long bolts which hold the light assembly to the caravan I heard a quiet click from the interior and now the outer upper bolt will not engage in a thread and just turns on its own. I suspect that I have displaced a captive nut from the inside of the light fitting. There is no obvious (to me anyway) way to access the back of the assembly. Beneath the bed it is all boxed in, likewise from underneath the rear of the van. How do I get to the back of the light fitting ? In addition I noticed that all the terminals connecting wires to bulb fittings were clean and dry. Does anyone use any treatment (vaseline, WD40, silicone grease etc.) to keep the conections good?

thanks in anticipation, Mick Rumble