One important hing to consider on our boats, which, admittedly, Ken is not specifically familiar with: just above the electrical panels is the stanchion with the waste tank vent.
While the area behind my panel is dry, dry, dry, I have seen some that look as if a fire hose had been squirted into it.
That said, for what you are doing now, ITWMB, I wouldn't bother to heat shrink each connection. IIRC, all my terminals are facing down, with the wire going UP to them. My larger issue is that they didn't use ring terminals, but flanged spade connectors!
This should get you by until you decide what you want to do when you replace your panel next year. The wiki has some very good illustrations of what, for example, Jon did with his. A great writeup with tons of pictures.