Panorama image size

Johan is exactly correct. The massive increase in filesize is caused by the original files being in a Bayer Mosaic arrangement, so each pixel is only a single value at 12 or 14 bits precision. The resulting panorama will be in full R,G, and B for each pixel each at 16 bits precision (I am almost 100% cerain it is to make sure you don't lose info), so 48 bits per pixel or a 4x increase in required space for just a single image. Combining a few images, you easily end up with a factor of 8. The very efficient lossless compression in dng (typically much better than in native raw files) helps but the fundamental issue is the demosaic that has to happen before you can stitch, tripling the required data and the increased bit depth leading to another factor increase. That's before any stitching has happened.

So, I did find one source that states 32 bit. have no idea why reports as 48. Have not yet gotten off my rear end to test. 

Also, even though it apply's to import, in preferences, file handling, import DNG creation, the option to embed original RAW file, could that cause the Photo Merge DNG to include the original RAW file? Something to test

Thanks for that, I didn't realise that but that's around a 2.3 increase in bit depth but that still shouldn't in crease the file size that much, in the screen shot example the pano is around 239,000,000 pixels in size, if I multiply by 2.3 it should result in a file size or around 500MB rather than 705MB.