For a fairly small load like that, there is a way to get a pretty good estimate of the weight.
1. Start with the tow vehicle loaded like when you'll be towing, but with the trailer unhooked.
2. Measure from the top of the bumper to the ground with a tape measure. Record the result.
3. Get several friends around who can help. Weigh each friend, and then have them step on the bumper. Measure the height from the bumper to the ground and record it.
4. Repeat steps 3 with several more friends, adding one at a time until four or five friends are on the bumper.
5. Have the friends get off the bumper and hook up the trailer. Measure the distance from the bumper to the ground.
6. Compare the bumper sag with the trailer vs. the friends. This will give you an approximate tongue weight.
For example, if three friends all weighing 200 pounds drop the bumper 2 inches, and your trailer drops the bumper 2", you'll know the tongue weight is approximately 600 pounds.
This is the "shade tree engineering" method!
Jim