Hi readytohittheroad,
If you go to the Heartlandrvs.com website, click on Road Warrior on the left side, then click on Weights and Measures at the top, it'll show you all the RW models with GVWR and empty weight. A 310 shows a GVWR of 15,500 and empty weight of 11,055. The difference is how much stuff you can carry.
You probably won't get the entire 4,445 suggested however. The empty weight is the design weight of the basic coach with no options. Plan on the out the door weight being perhaps 1000 heavier. So you might get around 3,500 capacity for your stuff, water in the tanks, fuel in the fuel cells, and propane. If you know how much your Harleys weight, you can figure out what's left.