We use corner fleece forests- & improvised ones too.
The clips are fine for Guinea pigs.
This is a photo of part of a set up away from home- I made the fleece forest from fleece scraps- it’s just tucked into a grid used on top.
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View attachment 238994
Here’s the random assortment of things we use for attaching corner forests or pegging blankets around the outside to help prevent drafts. Clothes pegs in our holiday bag have been very useful. We just make sure clips/pegs are only used near the top of the grids.( we use CC grids).
After thought…..
cardboard boxes with doorways cut out are very handy as houses on holiday too.