To help keep seals longer, it pays to store the glider such that the controls are "neutral". Horizontal tail is usually covered by the mount/holder for it when disassembled.
Flaps and ailerons can be covered by small trailing edge "cuffs" that center the control relative to the fixed wing trailing edge on "most" gliders. The cuffs are thin sheetmetal bent almost in half that just slip on. A layer of tape, etc. inside prevents scuffing the gelcoat when installed.
Make the cuffs as cheap or fancy as you want.