For the CD noises, try a ground loop isolator. See this thread - http://www.airforums.com/forums/f450...xed-39321.html
It worked for me.
For the mattress - Most RV dealers have them. For your trailer, I am pretty sure it's just a "short queen". Both sides are straight, right? If you want a better mattress, there are usually local companies that can make a mattress to pretty much any specification you want. Keep the weight in mind though. Super nice foam mattresses are pretty heavy.
For the lock, the first thing I would do is try some lubricant. There is a lot of stuff sold just for the purpose of freeing a sticky lock. Most contain graphite and a light lube or carrier of some sort.
Can't really tell you much about the pine needles. I wouldn't worry too much about them but the pine tar or pitch may be a pain to get off.