This is a mesh panel from linens and things that we bent to originally make a tunnel. Then in a flash of creativity, we decided to attach the tunnel against the edge of the cavy cage. You can't tell by this picture, but we attached it so that the open end of the tunnel was zip tied to the wall of the cc cage. It's completely enclosed. We had to use the tiny zip ties (we bought a big thing of them that had various sizes from Orchard Supply) but it's more secure than my stair railing.

It allows the air to breeze through so he doesn't get overheated during the day. At night I lay a towel on top to keep him warm. I shake the poops off the microfiber towel daily and wash once a week.

for the hot days I've been placing a large about 1ltr frozen water bottle on the top of the "penthouse" , (the mesh style cubes from linens and things actully have grooves in them so the water bottle doesn't roll off. then I lay a kitchen towel over the water bottle and sides of the "penthouse". I tried it without cover the water bottle and by end of day the ice has melted. When I covered it, the water bottle still had ice when I came home from work... The cold air falls downward into the little house when you cover it.