Check Your neighborhood if somebody doing glass or Plexiglas work and order piece of Plexiglas that fits exactly inside of your tank top and cover 2/3 of it if You use dome heat, or even 80-90% if You use only heat mate...
I had same problem before when i have BP in tank and piece of Plexi covering 2/3 of 20g long tank cost me 6$ and look way better than aluminum foil.

Occasional Misting will help too. Other thing what help with wy case as well was switching substrate from aspen to repti-bark. It keeps humidity a way better and looks cool as well.

Hope this helps.