Do they work well? What size of trailer do you use and for how many people?

Size is going to depend on many factors.

How many people you want to sleep.
Towing capacity of your vehicle.
Amenities desired from said trailer.
Ability or budget to store said trailer when not being used.

If you're looking for a "home away from home" like an indoor cook space shower/s%^ter. You'll need something sizable and also something to tow it.

If you're just looking to rough it without roughing it for 1-3 people and want to tow with pretty much anything skip the airstream look into a teardrop type rig.