I still use Blender 2.79. I model everything using Blender units, or meters. However, I treat meters as feet while I model, or 1 foot = 1 meter, 6 inches = 0.5 meter, 2 inches equals 0.2 meter.
When my model is complete, I center the 3D cursor (Shift-C), select the 3D cursor as my Pivot Center, select the entire model (A key), and scale the entire model to 0.305, which converts meters to feet. I also add 'scale' to the file name to know which one to export into Trainz.