Go once to a place that will weigh your TT unloaded, then once more loaded with everything including a full Fresh water tank. That would be your heaviest load. Check the weight of of your tow vehicle, including tools, full tank of gas etc. 1+1 is your max. You'll be good forever, within in a + or - at least.
Might even carry a couple of passengers in your tow vehicle to be on the heaviest side you may ever carry.