There are many designs for small sheds that will roll off on tracks or wheels. If you have such a large deck, then you can spare a few feet in back of each telescope to store a small shed. Roll each one onto the north side, to avoid sky interference. The sheds can be padlocked down to flush-set rings for security.
I set up a twelve inch Meade LX200 for a friend and am familiar with the sizes needed. If your telescopes are on permanent piers, the size of a shed is not very large. An internal plastic cover and a small incandescent light to keep out moisture, or a dry air system is recommended to keep a telescope in good condition.