Hey Tim,
I am moving your way in January. What part of Mid Tn are you in?
You can use the Musketeer as you have stated with no problems as long as you keep the box dry. It will work fine in fresh water with no issues. You could also go a little farther to protect it by encasing it in a large rectangular tupperware type container. You would have to cut two holes through the side of the container for your earphones and coil cable. You can putty the holes or there are some waterproof rubber washers that you can fit into the holes and pull the cables through. It won't be submersible that way but it will be protected completely from splashes, rain, etc. I am not a pro at that type of modification. You find some high dollar conversions that are completely waterproof on some other posts way back in Beach/Shallow Water. Or you can do the tupperware thing for a few bucks and be more assured that water won't get in your box if you are splashed, etc.
Check with Treasure Hunter on this forum. He has a converted Sovereign which is a high dollar conversion but very nice. He can tell you more about that set up. Here is a link to the thread where his is shown and there is another or two. You can see that these are a little over my head but well done.
I took the liberty of using one of his photos to show you here but go to the thread and you will see more pics plus some discussion on the topic.
http://forum.treasurenet.com/index.php/topic,179885.0.html
Here is also a pic of a cheaper tupperware type protection with an Ace 250.
Good Luck.
DaChief