Your gown should be cleaned as soon as possible, it can be rehung for selling, if you plan to do this within a few months.
But if you plan to keep either forever or until you have decided what you want to do with it, then have it cleaned and boxed. When bought to me I will spot clean it and then it is professionally cleaned before boxing in an acid free box with lots of acid free tissue paper,
There is a wonderful choice of boxes in different designs and colours so you can match your wedding theme or room décor.
These sturdy British made boxes will be a lovely keepsake and last for many, many years.