The Collaborative International Dictionary of English v.0.48:

Unsheltered \Unsheltered\
   See sheltered.

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "unsheltered":
   bare-handed, defenseless, guardless, helpless, unarmed, unarmored,
   unattended, uncovered, undefended, unfortified, ungarrisoned,
   unguarded, unprotected, unscreened, unshielded, unsuspecting,
   unwarned, unwatched, weaponless