I hope I'm barking up the right tree

I include the battery, and propane as part of the 1200 - 1500 lbs total I add to the dry weight of the Trailer. For estimating load and weight purposes I would use 1200 lbs for a small trailer (16') and 1500 lbs for a larger trailer (28'). This all becomes part of the "total weight of the trailer ready to camp". I than use 13 percent of that total weight to get to tongue weight. You can also shift weight to behind the axle of the trailer to keep your tongue weight down to the 12 - 13 percent range, which is generally all you need to keep your trailer stable.