A-liner is another option. small, easy to tow, and easy to set up and hard sided. Many have a minimal kitchen and just a cassette or porta potty toilet.
A liner doesn't have bunks, but the one a friend has has a slightly raised suspension for clearance (from the factory) a Queen bed and a couch that folds into another queen.
I bought a 7x14 cargo trailer to make into a small toyhauler for my motorcycles. I converted it to also have a drop down bed, couch, fridge, cooktop, shower, grey and fresh tanks. that size also could be converted to have a drop down full sized bed and a set of bunks at the back. 8x16 would IMHO be an ideal size.
The one downside of a cargo trailer is the weight. Most are steel framed including the side and top framing and a pretty stout frame. My 7x14 weighs in at almost 5K empty as converted.
