Answer. This can be a complicated issue. First, there are a series of state statutes governing the towing of vehicles from private property (here). They should be carefully reviewed before undertaking this process.
Here is a relevant portion of the law:
98.810 Unauthorized parking of vehicle on proscribed property prohibited. A person may not, without the permission of:
(1) The owner of a parking facility, leave or park any vehicle on the parking facility if there is a sign displayed in plain view at the parking facility prohibiting or restricting public parking on the parking facility.
(2) The owner of proscribed property, leave or park any vehicle on the proscribed property whether or not there is a sign prohibiting or restricting parking on the proscribed property.
Also, some cities and counties may have their own ordinances. The City of Portland, for example, has very specific rules (here). Gresham and Tualatin do as well. Plus, the Oregon Department of Justice has various consumer protection rules against “predatory towing”. (here).
For manufactured housing communities, I suggest going much farther than relying on state or local laws. If your community decides to do this, it should be clearly disclosed in the rules and regulations. Of utmost importance is proper visible signage, which can either be created by management, or provided by the towing company you decide to use. Make sure the company has a good reputation in all respects, and no records of consumer complaints.
If the violator is a resident, I suggest one or more warnings (following a protocol in your rules) before having the vehicle towed. Once towed, the car is impounded, and the cost of getting it released is not insubstantial, and the towing company has storage lien rights. If the process is not strictly followed, the owner could have a claim against management for conversion, i.e. the civil side of theft.
Fining is a much safer alternative, but must also follow community rules. The worst that can happen if the fine is levied in error is to rescind it. Making an error in the lead-up or during a tow, can be much more costly to management.
Fines can be enforced with a 30-day notice under ORS 90.630, so long as it is found in the rules. I suggest a warning notice first. Take a picture of it on the car, with the plate visible. Include the date and time. Mail a copy of the notice and the picture to the resident within 7 – 10 days. Use a certificate of mailing.
Make sure there is proper visible signage describing the proscribed area, the times, if applicable, and the amount of the fine.
If the fine increases on multiple violations, describe that, or reference the park rule. Do not make the fine punitive. If other communities have such violations, find out what their fines are. Always use the rule of reason; don’t impose a fine that most residents could not afford.
The issue of visitors is somewhat different, but rules may be enforced against the resident whose guest they are. That is why a warning notice should first be given. The notice and picture would go to the resident, who will, hopefully, warn their visitor about obeying marked No Parking signs.