Don't listen to BFL :), he is traveling with a big generator, of course he'll tell - go ahead, spend those amp-hours...
There is no limit in saving energy when you have to, i.e. when you don't have much of it. You have propane to make a dinner, AA battery LED lights, and if it's not freezing in trailer before you go to sleep, you don't need any 12V power. Consider a catalytic heater, in your situation this is an investment well worth it, will save both AH and propane for hot shower. With a whole 140 AH bank, this is 70 AH usable, more than you need for 5 days with cat heater.
Here is a recent portable setup of
2*50W panels hinged together, propped on pieces of conduit. Doesn't cost much. One 100W might be cheaper, but 2*50 is easier to store. As it's been said, you only need a thin #10 cable from panel to controller. People use landscaping cable if panels didn't come with MC4 plugs, otherwise you have to buy MC4 extension cable #10 and cut it in half, it comes in up to 100ft length. And a red-black booster cable #8 with crocodiles from controller to batteries - like the one that you have in your truck, cut the crocodiles off on the controller end.
