I've searched myself silly trying to get parking garages and/or lots to work but none will. Tried a bunch of them, among thoese I tried are parking garages of KingLeno and parking lots roads, I've seen people using those so I know they can work. I use the options "Enable more realistic parking" and "disable despawn". I use a lot of non parkingable roads and cars drive around a lot and then despawn which is normal TM:PE behaviour I believe.
I really hope someone can point me in the right direction