My tanks have lexan covers.

Same. No issues with light penetrating the lexan either even when I let it get covered in salt and dust and who knows what else.

Sump isn't covered but its in the stand and don't really have an issue with it sneaking out of the stand and causing issues.

Mine is a 325gal in-wall system with a 50 sqft equipment room. A 110 CFM bathroom exhaust fan blows out the hot humid air and a 4" hole in the exterior wall of the house allows fresh air to be drawn inside. Humidity doesn't exceed 45% but room temperature due to MH lighting climbs to around 30 C each day. I'm going to try a 300 CFM fan and if that doesn't work... LED lighting is in my future.

I was lucky, my house came with an HRV when I bought it. Never any humidity issues

depending where you live, ERV also an option

I have a glass cover on my tank. My sump is open and I have a opening in my stand so no moisture builds up.

shorts, tank top, and lots of corona:biggrin: