@kornacle
First, I am a former Hunter dealer and very knowledgeable about the Hunter water ballast sailboats now retired.
As you suspect, it appears the boat was sitting on the trailer which was backed into something.
The hull to deck is married together with a bead of marine putty at the transom only. It appears the crack occurred in the marine putty bead. First you need to open the port locker door in the rear berth and take some photos and post them here looking toward the crack area.
Outside, take a dremel with a small ball file at low speed to remove the marine putty and stop at the fiberglass hull and deck walls. Dremel down removing alll of the cracked putty and then sand with 80 grit sandpaper the inside of the fiberglass removing any remaining putty.
There are many different epoxies; however, I found that Water Tite epoxy was the most durable but well worth the money. Apply it with a putty knife forcing it in. You will need. Dry weather with a minimum of 64 degrees and let dry overnight. It may several applications as you do not want the epoxy sagging Then sand smooth.
Borrow a paint color chart from a paint shop or hardware store and match it up to the white color of the boat or close to it. Buy the spray can designed for outside plastic paints. Sand the entire hull to deck joint and wipe off. Then cover or mask off the transom. Spray three times and you are done.
If you need my help, I would be glad to advise via phone and your number would never given out. Private message coming your way
Dave condon alias crazy Dave