Yet another option might be to get to know your neighbours. You might find after a while that one of your neighbours is happy to let you park in their unused space whenever you care to with or without accepting your offer of rent.
I assume you have have parking on site that is perhaps uncovered or not allocated to any particular unit. It might be possible to propose a scheme whereby those spaces are covered at the expense of unit owners who get to have that space allocated to their unit. This could be done well to everyone’s benefit or it could be done badly and backfire. If such a scheme seems feasible do it with legal advice.