There are several lightweight travel trailers such as the Forest River R-Pod Travel Trailer, Aliner Travel Trailer and the Airstream RV Sport Travel Trailer.
Airstream also makes some other good light and easy to tow travel trailers that can be towed by as little as a 1/2 ton pickup.
The KZ Spree Escape Travel Trailer and the Jayco Hummingbird travel trailers are a few other good lightweight travel trailers that are under 3,000 lbs in weight.
Aside from that the lightest weight travel trailers are popup campers and teardrop travel trailers.