Inman was on his own after Radzinsky died (allegedly).
The Swan was well within 108 minutes round-trip distance of the Losties camp (Kate fetching Sawyer to fix the computer in 'Orientation')*
Henry Gale's balloon was at least a day's hike away from the Losties beach camp.
The Tail section crashed a couple of days march away from the Losties beach camp.
The 'line' (not to cross) was well over 108 minutes round trip distance.
The Pearl hatch (in '?') was well over 108 minutes round trip distance away.
The Black Rock (in 'Exodus') was well over 108 minutes round trip distance.
You've got a lot of work to do to explain how someone could gather the information on the blast door map without embarking on a lot of extended trips kitted out like Inman in his Hazmat suit!
Still, if Inman could find the time and resources to repair 'Elizabeth' (single-handed!), I suppose anything's possible to such a Superman!

THE OWLS ARE NOT WHAT THEY SEEM