The side of the tiny house that faces the tow hitch should be considered the windward side. The side that faces away from the tow hitch should be considered the leeward side. This is because when you tow the tiny house down a highway, the tow hitch side will face directly into the apparent wind and the other side will face away from the apparent wind.
Identifying these sides of the house is more than an academic exercise, it is a functional exercise. The siding on the windward side needs to be much more secure because it will frequently be faced with very high wind speeds!
The siding on the windward side needs to be fabricated out of solid planks that run the full width of the tiny house. There should be no butt joints on this side as these joints are weaker in high winds.
The leeward side is much more forgiving. There will be very little direct wind on this side and butt joints are allowed.
This side is sided by all the left over off cuts from the windward side. These pieces are simply set and fitted to one another, making them reach and fit the length needed.
You want to stagger the butt joints though, that way they blend in and disappear into the wall. If you set all the but joints in a single column, it will be very noticeable and will be considered rather unsightly.