Export tif image with 300 ppi

[Ofnuts]

72PPI is a default value, so probably your 72PPI is just  a missing print definition. However: if the file command doesn't show any print definition in an exported TIFF,

• re-importing the file in Gimp shows the correct print definition (I tried with a wacky value, to ensure it wasn't some default value being restored), so the print definition is somewhere in the file.
  
• The print definition is indicative, the important thing is the size in pixels. The print definiiton can be ignore/overriden at print time.