yes resample at a lower rate, consider sampling as mono.
You may be able to restrict the file size further by carefull choice of the file type - some storgae formats are leaner than others.
In effect its is exactly like storing an image, you can adjust the file type (blocky graphics work well in GIF & PNG, photos work well in JPEG & PNG), you cab adjust the qulatiy threshild in the JPEG & PNG to contorl how images are samepled & stored). And exactly like adjustign the quality, adjusting the sampling down bins information from the file, nor does adjusting up recreate more information.