Fuel Gauge Problem?

SO I get my "new" '96 C220 on the road after the mechanic fixed the fuel pump relay. This was the first time I got it on the road...MAN is this thing smooth!!! I am absolutely in love with it..and MB!!
While driving, I noticed the fuel gauge seems to have a short or bad electrical connection since while driving, it drops to "0" and after a while, jumps back up. No other gauges are acting up.
I noticed when the car first broke down (cranked but wouldn't start) the fuel gauge was "dead"..even after a fill up.
Could the mechanic have not secured the relay connections well? I know it could be a loose wire anywhere in the circuit, but I was wondering if there were other systems connected to the fuel gauge that I should be aware of when I start checking.
Slowly, but surely, I am learning about this great car.

Also, while I was at the parts store (new wiper blade), a passerby was telling me that he had one and they are extremely hard to maintain. He told me that MB electronics hate humidity and I should place those dehumidifying packets under the dash and other places. He also said tuneups averaged $400 and at 100K miles, a lot of the fuses will give out. He was aslo telling me that the car should be kept in a garage with a dehumidifier, since otherwise a lot of problems will arise down the road. This kind of alarmed me since I am on the Gulf Coast...the most humid area in the United States!! Not too sure how much to believe him about some stuff. I can see the fuses needing changing, but dehumidifying packets stuffed everywhere?