I will be visiting St. John in March and have already decided to rent a car while I'm there. I was just curious. Can anybody clue me in on how easy it is to park at the various beaches, etc...?

Thanks in advance!

I was there over Thanksgiving- so low season.
Parking was available at Trunk Bay, early in the morning, before the cruise-ship passengers from St. Thomas arrived. I found it was really only worth being there between 9-10 am anyway before it got super crowded. The Hawksnest Beach lots can get crowded as this is one of the first beaches you come to as you head north. Jumbie, one of my favorites because it was often deserted despite being close to town, has 4 spots for cars across the street from the stairs that take you to it. Cinnamon Bay has quite a bit of parking.
I could keep going...if you don't see a spot to park you can just head on to the next beach, I found the farther you get from town the less people there were.
St. John Feet Fins and Four Wheel Drive by Pam Gaffin has details on all the beaches and the more iffy dirt roads