Germination Issues?

What are you trying to germinate? Unless it's peppers/chillies/tomatoes/cucumbers etc. or anything that likes it hot, most things germinate OK at room temperature. I think a windowsill propagator like that would cook plants on a sunny day. I germinate lots of stuff on windowsills but generally uncovered unless it's seeds sown on the surface.

As far as watering goes, after I've filled the modules/pots with compost, I water very well before sowing then don't water again unless the surface is getting very dry.