I did mine at the local truck stop scale. Cost was $9.00 per weighing. Go in and talk to them before driving up on the scale so you both know what you want and need to do. I think you'll find they will be VERY helpful.
I did two weighings. One with the trailer connected (front and rear axles of the tow vehicle on the first two platforms and the trailer on the third platform), then, I unhitched the trailer so that it and the tongue support were all on the rear platform, with my tow vehicle still on the first two and had the whole mess weighed again.
This way, I got an accurate measurement of the total weight of the trailer, and my tow vehicle weight. Then the additional weight on my tow vehicle's axles with the trailer connected as well as the axle load on the trailer itself in the tow configuration.
- Jack