so many variations by location. in my corner of the world, my trailers don't register for any specific weight, just number of axles. The tow vehicle carries that burden for both tow vehicle and trailer. i currently have a half ton / 1500 series, assume +/- 7k weight with me, fuel, gear, give or take. truck rated tow capacity is 9300lbs if i remember correctly, so i register for 16k. rare chance i ever haul past 14k total, but went the extra 2k just for good measure. if i were to get weighed, who knows where each axle would come in, but i'm willing to gamble. you really need to look suspicious to get the scales called in on a standard pickup towing a trailer, but i can guarantee it has happened...
Many people / businesses from other states register their trailers here due to the low cost. there are a handful of privately run statutory agents here that you can register through. also allows you to register for longer terms. i usually do 5 years at a pop, but you can do more.