Big Rig friendly gas stations - West Yellowstone ?

I wouldn't assume. Most of the RV-friendly gas stations we have found outside of West, in Island Park, Idaho. The ones I am aware of in town are mostly pretty small and sometimes crowded. We usually fill up (gas) when we're unhitched, or somewhere in Island Park. Prices will vary; we've sometimes seen prices higher in West than inside the park.

I like the suggestion to check Google street view.