I tried to explore using a Tacoma but any kind of camper puts the unit at a heavy weight and about 12mpg.
Agree w/ everything above. I have customized an old fiberglass shell from an old 1980 toyota RV to fit a ultra light duty flatbed Toyota T100 (tundra same thing) putting a lot of effort into keeping it as lightweight with the materials at hand without spending any money (probably have around $7K into rig which includes the truck!). While it does manage to come in under the GVWR and can be done, it's discomforting knowing that it is operating at close to carrying capacity (and for sure OVER on the longer camping excursions). And I don't see how the Tundra (esp with its truck bed) can be a platform for anything other than a pop-up camper shell.It's difficult to keep a camper light... The Tacoma, for instance, may have 1400# of payload, but that quickly goes down the drain...
For me, I am building a hard sided pop up camper to minimize dimensions, and will be putting it on a regular cab F250 diesel.

Ya!I wish we (North America) had smaller high payload diesel trucks available...

My v6 Tacoma with a Four Wheel Camper got almost 18 mpg average over 3000 miles of traveling. Some with the (underpowered) four cylinder Tacoma have reported getting just over 20 with their Four Wheel Camper mounted.
Just food for thought.
...Don't know the durability of the E350 compared to the F350....