I hear this is new. If you are getting a tag for your trailer in Broward county (maybe the whole state) you need to get it weighed first. $10. If you have not had it weighed already or the weight on the previous registration.
There are a few local companies that will weigh it for you. Again $10.
I have done it many of times. If you are registering a trailer that you either built or don't have a registration you will have to have a weight slip from any certified weight scale. If you are going the homemade route, they will have you fill out a short form asking where you got the parts.... which is very simple "Northern Tool". It is a very easy process and pretty cheap as well.