First, I'd like to thank the members here who gave me some great advice as I was going through this build.
The total finished weight of the teardrop is a mere ~170lbs and it tows behind the vintage Vespa fairly well. The limitation is actually the trailer...when I thought for sure it would be the bike. The 150cc 2-stoke motor pulls strong and the manual transmission definitely helps while towing. Even the bike's dual-drum brakes do a good job stopping the trailer. The limitation is the solid axle on the trailer. When I hit a sizeable bump or pothole it will sometimes bounce the trailer wheel(s) a couple inches off the road. I found that adding some cargo over the axle helps...as well as trying to avoid road imperfections.
I had the trailer out over the Thanksgiving weekend for some camping. Video below. There's closed caption commentary if you click the "CC" button in the YouTube viewing window. There's also a link in the description box if you are interested in seeing the "tour/reveal" video.
https://www.youtube.com/watch?v=wzGYiUVkqqM