Is it necessary to have a shuttle rsvp on wedding invite?

Hi all!
So my fiance and I booked a 50 seat coach bus that will shuttle guests staying at our blocked hotels to and from the venue. One hotel is 15 mins from the venue, the other is only 5 mins. I think we will be OK shuttling guests from the venue back to the hotels because we will have the bus pick up guests at 10pm, 11pm, and midnight; however, my only concern is whether the bus will have enough seats available to take guests to the ceremony. Going to the ceremony, the bus will only pick up hotel guests once because I don't think it will have enough time to return to pick up guests a second time. We're inviting about 195 guests, but I'm guessing 150 will actually come.. There is enough space to park at the venue and they do allow guests to park overnight at least.
I'm just wondering if you guys think I should have guests RSVP whether they will use the shuttle, so we can ensure there will be enough seats for guests going to the ceremony? There's not enough space unfortunately to put it on our RSVP cards, but I'm thinking of having the invites direct guests to view our website for further details and the transportation info will be on the website - and I would put our contact info where they can reserve their seat for a shuttle to the ceremony? What do you guys think?