Hi Portliz
Post is asking how to hold the chairs in an upright position.
My suggestion would be to simply attach a strap (could be Velcro or buckle) to the wall. Self tapping screw into a stud, washer will enlarge the screw head and avoid it coming through the strap material.
Simply wrap the strap around the chair (or chairs) and they should hold standing up.
Canvas chairs are light and should not create much stress. Weight would be on the floor through the legs .
I would try using a front wall as I would suspect you would have more motion when stopping vs. when taking off.... this way the pressure would be on the wall not the strap.
Easy to remove the screw/strap when trading in the unit leaving little evidence of your customization project.
My 2c worth.
GPG
GPG ๐
2014 Ford F250, 6.2L, 4.30 Ratio, 6 speed
2014 Cougar (by Keystone) 327 RES