Using cdsf’s splitter spreadsheet I generated some 1 degree tiles of southwestern US. MP sizes for each tile varied from 250 to 300MB and IMG file sizes ranged from 17MB to 24MB. I can install these in MapSource, but when I transfer them to my OR300 they don’t appear on the select map page as maps that I can activate/deactivate.
File size wasn’t the problem. I had two maps on my OR300 with the same name, and only the first one loaded showed up.