In one strata I am involved in some folks wanted a storage facility similar to what you are after. Most residents as well as the committee were ultraconservative in their views.
So one owner suggested that she understood every owner had a right to install a cabinet in his/her car space, which may be a double deck (ie affixed to the wall and a car parked between the cabinet and the edge of the allocated car space (restricting cars to be no more than “medium” sized) or installing an over car cabinet (again, fixed to the wall, but this time allowing the car to make full use of the car space as the single deck cabinet would be above the car and not using more than a few cm of the car space for the installation).
In both cases the installation made full use of the car space’s width.
A compromise was reached that only one installer/supplier was to provide the cabinets and two models of cabinet would be permitted (double and single deck), so that the garage would remain looking uniform.
So far plenty of owners have installed such cabinets, which can hold a great deal and, should you ever relocate, they can be disassembled by the installers.
From memory the cost of a double deck (supply & install) was $4k
When proposing this to your committee, obtain brochures and prices, so they have something to tangible to consider. Point out the advantages I list above.