Mpffff we do it all the time at our summer house as it gets down into the fall. Modern etilrecc heaters are rated for direct contact with flammables such as paper and cloth, have no exposed heating elements and for the most part include tip-switches, thermostats, fusible links and similar safety devices. That being written, common sense (which isn't) prevails. Look for a ceramic-type heater that is thermostatically controlled, carries the appropriate certifications (UL if US, CE or CA or similar if elsewhere), place it well away from clutter, cloth and clothing, never use an extension-cord with it and rest easy.