In reply to Catriona:
When I last passed Glenmore (6 or 7 yrs ago) the small lean-to at west end was open and could have given a dry basic shelter.
There are at least 4 other bothies south and west of the Schiehallion, on a fairly steep sliding scale of amenity. A 5th (Glen Sassunn) is too ruinous to qualify.