The town of dunedin is a nice, old florida town with some good restaurants and window shopping. But, you will be done in about a half a day. The closest beach is either north to tarpons springs or south to honeymoon island. ( About equal distance) I don't know anything about rv parks as we have never had a need to stay over there, we only live 45 minutes away.
I assume you want to bike or walk the trail? It goes for miles as you may know ( owned a house on the trail some 13 years ago.)
You can always spend a day at the tarpon sponge docks or head more south to clear water. That entire coast is very nice and has many spots for relaxing and enjoying the best of Florida.