Rob, the Terry Resort M18-D (according to NADA) weighs 2880 lbs dry. Following the 15% tongue weight rule, that should put the dry tongue weight at about 430 lbs dry give or take a few. If they calculated it at 12% it'll be a little less... around 345 lbs give or take. Filling the propane bottles and loading it up probably will make it a little heavier (some of the tongue weight will be unloaded by water in the tanks and other trailer load... think of the axle as a fulcrum and how weight distribution affects a teeter-totter) Class III hitches are rated for 500 lbs dead weight and 1,000 lbs with a WD hitch. While technically within the dead weight limits for a bare ball, you'll definitely want to use the weight distributing, anti-sway hitch for it. You'll want to adjust the hitch setup so that both the truck frame and trailer frames are level (or as close as possible) when it's hitched up. Every hitch mfgr does that a little differently so how you'll do that will depend on what brand of hitch you actually have.
Anti-sway is a whole 'nother issue.
Let me know if you have any questions.
Roger