Believe it or not, a sleeping cat will fit between the roof of a van and the outside edge of the penthouse roof with the top down. They do not like it but they do fit.
Be sure to check for critters before closing the top.
Read detailed trip reports, see photos and videos on my travel blog, luinil.com.
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Current van: 2002 Ford E350 extended body camper with Colorado Camper Van pop top and Agile Offroad 4WD conversion.