Gary was his usual diplomatic self, and correct. I am more basic numbers oriented.
First IGNORE DRY WEIGHT! When you go camping, you will have filled the Propane tanks, added a battery, loaded sheets, blankets, pillows, clothing, shoes, towels, soap, shampoo, food, pots and pans, silverware, plates, glasses, cups, lawn chairs... USE THE GVWR FOR THE CAMPER. Your actual weight will be much closer to GVWR than it will dry wt. If you can safely carry the GVWR and pack light, you have a safety margin.
That 5000# Max tow assumes NOTHING in the vehicle except two passengers at 150# each and a full gas tank. Every pound above that - including the WD hitch (80#) reduces the max towing weight pound for pound. This is where that 10% - 20% reduction of max tow comes in to play.
Another way to do the calculation is to start with the yellow placard Gary referenced on the driver door latch post. It gives the max load the truck can carry (Payload). Add together the weight of all passengers (no allowance here) and cargo including the WD hitch and 10% - 12% of the GVWR of the trailer as best estimate of hitch weight. This number MUST be LESS than the truck's PAYLOAD.
The Ridgeline is a GREAT little vehicle. I LOVE Hondas. I have owned several and currently have a Civic. However, the Ridgeline is designed first for passenger comfort, nimble handling and good fuel economy. It is great for weekend trips to the lumber yard. It is not designed as a heavy hauler. As such, the trailer it can safely pull is very limited compared to a F150 or 1500 pickup. Personally, I would stay under 4000# GVWR for the camper.
DO NOT trust the salesman. Here is why.
http://www.rvforum.net/SMF_forum/index.php/topic,90933.0.html