She is coming from NY and there is a good possibility her question could have been WPB to Key West and I know for a fact overnighting is allowed in WPB.
OP, you stand a better chance of finding a CG in Marathon... dry camping is NOT allowed anywhere in the Keys. Day trip to Key West in your class C from there although going there is not high on my list of things to do... especially with small grandkids as there are too many fruits and nuts on display. Also do not go the week before and after bike week at Daytona unless you like load exhaust noise 24/7.
If you overnight in WPB I would get on the turnpike there by going a little further west on 45th to Military Trail and then south to Okeechobee Rd and west to the turnpike. You will get a bill in the mail based on the RVs tag.
This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
Sold 04 Dynasty to our son after 14 great years.
Upgraded with a 08 HR Navigator 45โ...