[Rhodes22-list] GPS and Depth Finder

[mputnam1 at aol.com]

As I mentioned in an earlier email this evening, I just attended my first boating safety course, where the instructor (a power boater who spends most of his time on the Chesapeake Bay) insisted I needed a GPS and a depth finder.  
 
I didn't see anything about this in the FAQ, so I thought I'd raise these questions here ...
 
I will be spending most of my time on the Potomac River (I won't be trailoring, as I have a slip on the river), although I hope to be spending a weekend here and there exploring downriver in areas I won't be familiar with.  
 
Stan seemed pretty confident that I wouldn't really need a depth guage, given the centerboard's ability to alert me to shallow water ... and I don't remember what he said about GPS.  
 
Anyway, what do you all think?  Since my recycled boat is still at GB, it would be far easier for me to have them install a GPS and depth finder now, rather than trying to do it myself.  And the best reason I can think to have a depth finder is to help me calculate, from a safety perspective, how much anchor rode to use ... rather than trying to use the rode itself to judge the depth.
 
And how about GPS?  I've heard there are combination GPS/depth finders out there (I'm planning a trip to the neighborhood West Marine).  If I were to get a combo unit, where would you recommend installing it?  The recycled boat I'm getting already has a compass installed just to the right of the cabin door (on the cockpit side).  Maybe I could install it just above the compass, but are GPS units waterproof?  Should they be inside the cabin where you can't see it?  That doesn't make sense to me.
 
Thanks in advance for any suggestions.
 
-Mark