Yours is different from Bob's pic in that your main frame rails travel down along the inside of the wheel wells, whereas his pic shows a frame where the main rails travel outside of the wheels.
Yours would be much, much easier to narrow if you should choose to do so. All it would take is making sure that those angled tongue members tie into the main rails really well, and cut the rest of the outboard stuff off.
However, I would consider another, third, or perhaps forth option.
How about building the cabin between the wheel wells and having a deck with storage boxes round the outside perimeter (3rd option), or building the cabin out partially over the wheels with just half width fenders (4th option).
On TPCE I have yet to decide how I will secure my axe and shovel (some forest areas require you to carry an axe, shovel and bucket). Since I am building with a mild off road theme, I would welcome that extra cargo capacity outside of the cabin for easy access storage.
Good score, and good luck!
