This my friend is an extremely common complaint on this forum. I see the archives only go back a few days for some reason, so I can't copy and paste what I just wrote, but here is the jest of it.
In my case solar blankets bought at Cabelas for about $10 each solved the problem entirely. The sheets fit perfectly over the roof of my bunkends and were easy to attach with strong paper clips! There are eylets so you can also tie a small rope. Shiny side up on hot days to keep heat out, dark side up on cool nights. If budget is not a concern you can mail order popupgizmos which are custom-sized solar blankets equiped with bungy cords.
Condensation is greatly reduced that way, and the bunkbed is much darker which is useful in early morning. It's helpul to keep one or two window corners open in the bunkend to evacuate the moist air we breath out through the night.
For cold nights, Reflectix sheets cut to the size of windows and slipped from the inside between the window pane and the bug screen work very well to keep the space warm. Also, with the Roo you get the added benefit of heated mattresses.
Bruno, Carol, Thierry and Julien
Sankei the fox terrier
Starla the Gordon setter
97 Dodge 2500 4x QC diesel
2006 ROO19