Last time (first time) on island we took the passenger ferry as our rental company didn't allow us to take car over.
In looking at prices/convenience I think it makes sense to take car over on car ferry. Unless Im missing something?
We want to go to truck bay then walk around and eat in the little town after.
Should I buy one way fares so we aren't pinned on using one ferry over the other on the way back?
Buy the round trip. The only barge that does not allow ticket exhange is Boyson, You can go over on Global Marine and come back on Tuglife. See the ferry schedule on the above About St. John link at top of page.
You should also check out Annaberg Ruins while in STJ. If you buy admission to Trunk Bay,
you can use same ticket to visit Annaberg for free. Amazing Views and Sugar Mill ruins.
Lots to do so get an early start. Be sure to make it to barge in plenty of time to get there and back.
They get quite busy during season with everyone coming and going. Enjoy!
I'd go for the one way tickets for total flexibility. The difference in price is only $10.
It absolutely makes sense to take the car barge. Pack up your vehicle with all your gear and a cooler and enjoy a day of exploring! Enjoy your visit!