I used to store them under the mattress and salon
cushions - you can buy large plastic sleeves to protect them. Not a bad solution.
I then built a 5 sided teak
box which is set on berth (after cabin) next to a bulkhead and then attached a piano hinge so it can fold up against the bulkhead. The box is a few inches thick and has pad eyes and bungy chords to hold the chartssecure when opening or closing the drop lid chart storage. This also allows me to look at them "comfortably" and there's a light right above for the berth. It only took a few inches from the length of the bunk, and adds a lot of convenient and accessible chart storage and it's attractive too. The box is held in place by two ss eye bolts which act as pins a hole is drilled from each side at the top into small blocks which receives the eye bolts. They are easy to remove and quite secure.
If you have a similar location this works!