Try Krylon Crystal Clear artist fixative, #1303 or 1305, to fix the tissue instead of dope. It is less toxic than dope but should still be sprayed outside. A couple of misted coats should do to seal the tissue. I have models that I built in 2004 using Krylon that are still flyable.
Airbrushing acrylic paints or acrylic artist's ink over Krylon works very well. Krylon fixative is water resistant, not waterproof as dope, so the large load of water carried by the acrylics will cause tissue to sag after spraying but it will tighten back up again in a few minutes to hours depending on the temperature and humidity. Obviously, you have to let it completely dry between colors and changing masking. You can mask with airbrush frisket or Guillow's tissue sprayed with three or four coats of Krylon then cut as masking and applied with a repositionable glue stick (Post-It note glue).
This Guillow's 500 series Spitfire is an example of a model done this way,
Hope this helps.