I'm in northern Europe, so I wouldn't say it's very dry here. But during winter the RH can drop to 30% if it's cold outside. Then humidifying and using a PE sheet really helps.
I have a simple humidity chamber with a saturated solution of salt (NaCl). And sometimes steam over a sink with hot tap water.
Another trick is to sandwich a thick humid paper behind the print in the printing frame. Especially helpful if you are printing on thin papers that can't hold much moisture themselves.
Thanks for the tips.
At first I had all kinds of problems trying to coat this thin paper. Fell upon some steps which are working, at least for the time being:
1) Pre-wet the paper (torn to size with a thin border) on a sheet of glass with distilled water, making sure to brush it out flat (moving from the centre out works best, after 'draping' it gently into place) with a light touch and a hake brush until it has an even sheen.
2) Pat it dry (about half way) with paper towel.
3) Measure out sensitizer and brush it evenly onto the whole sheet of paper, right to the edges.
4) Place under a fan in the dark for about a half hour (typically a cup of coffee, tea, Photrio rummaging session, or doing the dishes) until it's dry. It stays stuck to the sheet of glass but peels up easily.
The extra water in the pre-wet step doesn't dilute the sensitizer because it evaporates off...its only purpose is to flatten and prepare the paper for the sensitizing step.