An interesting thread...
I lived in a normal house during the summer until I was 8. The last 19 years has been a combination of living in small spaces.
I have spent most winters living on our sailboat. Not sure the exact s.f., but it is 33 feet on deck, and 12 feet at it's widest point. All but the last 2 years we were a family of 4, and my dad's goal was as remote as possible. Many months we were on the boat with no option to go ashore, for days/weeks at a time. We have spent a total of less than a month at a dock or marine since we moved on the boat, when I was 4.
Part of what helps is we have 3 living areas. The main cabin, with 2 settees (built in seating), a large fold up table, 2 bunk beds and galley. The cockpit, with settees for 6 people comfortably. And the aft cabin. Which has a larger than full size bed, and no seating. Lots of storage everywhere... under every bed/settee cabinets and shelves etc. There is a bathroom with a door in front of the main cabin, then more storage (sail locker), then more storage (chain locker). With 4 people (2 teenagers, 2 adults) it was fine. I don't remember thinking we needed a larger space. We had guests a few times, as many as 4+(our 4)=8 for a week or so... it was getting pretty tight on board during those times.
We can carry a lot of a things, 2 inflatables, a sailing dingy, full dive gear for everyone, fishing gear, 2 outboards, a complete extra diesel engine, 220 gallons of water, 160 gallons of diesel, multiple head sails, storm sails, spinnaker, compartments full of extra gear and spare parts along with enough room for clothes and personal belongings, food etc.
It takes a concerted effort to keep things put away and pickup up, so as not to overwhelm everything.
You always had to get rid of something if you wanted to buy something new...
During the summers I lived in an RV (34' Airstream trailer) in the mountains of southern colorado. In a lot of ways, there is less room in the trailer, even though it has a larger foot print, you don't get the deck, or really separate areas.... but, you can always just walk out the door to get away.
We started traveling playing music full time when I was 14, my brother was 12... my parents bought a cab over camper, to use as their "room" while the airstream was our living area. We did that for 10 years.
My parents are now living in a house (dad is rebuilding a '69 jaguar xke), I parked the airstream, and I have downsized to just the camper. 8.5 months a year, with the boat being the other 3.5 months.
With 2 of us living in the camper (brother and me) it works, we are very limited of what we can bring, but the simplicity of being able to drive to our shows, play, then drive straight to our next show, stopping wherever, is great. According to my measuring we have 68sf of space, plus a queen size bed over the cab. We have a kitchen with stove, bathroom with shower, hot water, refrigerator, couch with table, and the aforementioned queen sized bed. There is a real lack of storage, and space utilization is good, but not perfect.
In cold weather, it does OK... We spend 2 months a year hunting above 10,000 feet in Colorado, plus visit the PNW for Nov/Dec... Condensation is better of the stick built camper vs the aluminum airstream.
The Airstream was $11,500 (in 2008), the camper was $3,500 (in 2004), the boat... well... it is a boat. Currently it costs about 3k a year to maintain.
I am shocked by the prices I see on these tiny homes. And new RVs as well. Especially the class B vans, $120,000+? for less room than my camper? No 4wd? I guess someone is buying them, but I struggle to see the value. Even at a theoretical 50% off, used price... Plenty of options for 1/3... 1/4... even 1/10 the cost. I see the same trend with tiny homes... lots of pre-manufactured options for much less. Especially considering land isn't included, and they suffer from the same zoning laws.