Tried to make some more trials but not happy with the quality of the mask I'm able to create using my cheapo Dell laser printer. In order to make a truly opaque mask a high quality printer is needed.
The specs for my printer state:
Print resolution
600 x 600 dpi (Up to 2400 x 600 dpi)
Not sure why the resolution is higher on one axis vs the other for high quality print mode but I assume this relates to idiosyncrasies of the hardware. At any rate, more than 600 dpi is needed in order to make a good mask I think which means I need to find a better printer.