Why reinvent the wheel?
A well chosen family car pulling an Airstream (or one of the older competitors as I do) can use less fuel with better space efficiency. And it can be ready to travel shortly after purchase. One of these is not "old" up to about 25-years. And at that point just needs refurbishment.
I use a one ton Dodge. Pulling my 35' trailer is 15-mpg at 58/mph in the South Cental US. Solo, not below 24-mpg same conditions, empty or loaded, rain or traffic.
The TD SUVs from Europe can do close enough to 30 while towing. The small cars with a small AS over that.
The aero qualities of the trailer preclude the need for a truck (with very few exceptions).
Airstream Trailer & Motorhome Owners Community is a wealth of info.
The link in my signature shows an earlier trailer sold.