OK all these ideas have me thinking. PoE is an interesting idea. Same with the NS2 on the roof. But I am thinking cheapskate and how can I get the hardware I already have to work.
I stumbled across a thread on another non RV related forum about weatherproofing a wrt54g. The leading answer was to go to Lowes, HomeDepot etc to the electrical dept and get a plastic outdoor electrical box that it will fit in.
Here is where it gets interesting... maybe... when inside the trailer, you probably do not need the wrt54g to actually be inside with you, you will likely still get good signal a few feet away on the other side of the trailer wall/roof. The important part is the reception from the outside for the wifi you are trying to relay from.
So a variation of RLS7201's setup. You use a PoE Splitter/Injector pair (I happen to have an actual Linksys pair specifically for the wrt54g. Put the injector inside the trailer, connected to power but not connected to downstream network, you than run PoE/Ethernet cable from the powered port of the injector thru the roof to the PoE splitter to split off the power again to run the wrt54g, but again with no downstream network connected. You only use the injector/splitter to deliver power not network. You then mount the wrt54g and PoE splitter inside a weather proof electrical box directly to the roof or Antenna mast. If the box is not too big/heavy using tin screws to mount it directly to the antenna mast maybe the easiest solution.
OK maybe a little half baked, but suggestions, thoughts, improvements, criticism, laughter???