Well, the forecast is for rain the next few days. Do you think a chrono will give readings if I block its view of the bright sky by covering with plywood? I'll call Oehler and ask them, too.
Plywood will block too much light. Try Saran wrap to protect each of the lenses from excess water. This fix should still allow enough light for a reading. Water getting into the lenses (if it does get through the wrap) will not permanently damage the guts under the lenses.