For me and my Scamp
13 I use an imaginary line on the floor where the axle is. I pack as little as I can on the backside of that line towards the back of the trailer. My water tank resides back there so there is already a fair amount of weight
back there to offset the balance with the trailer. Pretty much just blankets, pillows, and sleeping bags and other very light
weight items in the back.
In front of the imaginary line towards the tug anything goes within the weight capacity of your trailer. keep it heaviest close to the axle and weight down low. If you have an open floor plan where stuff can shift around keep this in mind when packing. You don't want stuff sliding to the back of the trailer upsetting the balance of the trailer. Just remember the last thing you pack is the first thing you unpack. Usually a tote with all your hook-up needs. Things like the leveling blocks, wheel chocks. Tools to change a tire and level the trailer. The last thing you want to do when arriving at a campsite is to have to unload your whole trailer and search for the equipment needed to level the trailer and unhook your tug.
We pack with us allot of comfort junk and really try to keep the trailer pretty much empty, so if we had to stop and sleep we don't have to unload the whole trailer. Our tug pretty much carries all the extra stuff. Whatever you do don't tow a dancing trailer, if the trailer isnt steady as a rock behind your tug stop and readjust your trailers balance. Running a poorly balanced trailer is a serious accident waiting to happen.
Learn how to use your brake controller to steady a swaying trailer. Slamming on the brakes
in your tug while the trailer is swaying can make the situation worse. Learn what to do in advance so you are mentally prepared when things don't go as planned.