We will be disembarking from the Ocean Princess on August 3 in Dover. Since our flight is at 12:35 pm that day, we are concerned that the motor coach is going to take 3 hours to get us to Heathrow. Does anyone have experience with optional transportation (reasonably priced) to get us there for the 3 hour advance required to check in? Is private cab the only option? Train looked "iffy".