Well...not knowing much of the VTT thing side of it. But if you know roughly what size this should translate to pixel wise, you can adjust the export (to png etc) through the TOOLS -> OPTIONS setting, select the BMP, JPG, PNG buton and then tell it the MAXIMUM IMAGE DIMENSIONS that the exported file should be.
Finally, then SAVE AS using the Rectangular BMP/PNG/JPG selection, and select only the part of the image that should be the image. This is the method I used when I was doing the maps for THUNDERSPIRE/PYRAMIDS/TROOLHAUNT etc.