For us, the truck has to come first. The truck we buy will determine how much of a trailer we can pull. 

Right now, we own a Chevy Colorado. It has a towing capacity of 7,000 lbs. Which means that we can haul a trailer as large as about 28 feet, if it's a "lite" version. The Bullet at left fits into this category. It is 28 feet and has a dry weight of about 3500 lbs, with a carrying capacity of 1300 lbs.

If we were to buy a 1/2-ton, 3/4-ton, or 1-ton truck, we would be able to haul 9,000 to 11,000 lbs. Which means we could get up into the 30-foot trailers.