secure against the weather the cover material is preferably silver coated to reflect sunlight it has been found that a woven polyethylene sold under the trade mark fabrene is suitable both for the lining and the cover provision of the lacing 31 permits the angle of the cone to be varied in accordance with the angle of repose of the material stored the lacing is fed through rings 46 so that tightening of the laces causes the cover to tighten in conformity with the cone angle of the stored material m along the bottom edge of the cover 30 there is a series of regularly spaced semi circular ears 44 each of these ears 44 includes a grommet fastener 33 fig6 d for attaching a tie down rope 45 thereto the grommet fastener 33 includes a button 34 which is surrounded by the plastic covering material 37 of the ear 44 a ring portion 35 of the grommet fastener consists of a large diameter opening 40 and a small diameter opening 39 which are joined by a neck portion 38 the fastener is assembled by inserting the button 34 with the plastic cover material surrounding it through the large diameter opening 40 of the ring 35 and then laterally moving the ring so that the button and surrounding plastic move through the neck portion 38 and into the smaller diameter opening 39 of the ring the plastic material is thus caused to bunch which together with the reduced neck portion 38 enables the ring to be held in that position the tie down ropes 45 are attached to the large diameter portion 40 of the ring and are tied to the top.