just a thought ... my husband had to access the underside of the 5th wheel... which has a undercarriage. that "flap" he taped up time and time again after he passed away my sil was taping and had a brain storm used zip ties to hold the flap closed we no longer have tape flapping away... so if you have an under carriage you could put holes in it and secure the x pens to it with a zip tie the come in lots of different sizes... and then again perhaps it wouldn't work but sometime to look at
my windows are on the side of the bed never have had them above the bed... don't think I would like it either when it's warm enough I have both open hasn't been warm enough yet
sheila