Maybe call them for reservations and ask about restrictions then. While it may be frustrating arriving someplace and find out they have a restriction, I would think it would be equally frustrating arriving and find out they have available spots for you at all.
You know that you have a vehicle that is older than 10 yrs old and you also know that there are parks with restrictions. So you know there is a possibility of coming across such places. You need to do more planning to make sure you are not wasting your time. There is a park not too far away that if you go by the name with "motorcoach resort" in it, that you would think that a trailer is not allowed in it. We see them in it all the time. Mostly fifth wheels. So sometimes, it takes a little more than seeing a place in a book and putting the address in your GPS and going. With today's technology, Internet, and cell phones with unlimited calling, there's no excuse to be able to do more research. If you fly by the seat of your pants, you can expect a snag ever now and then.