I love pickling stuff, and fruit is no exception. The problem I ran into when I started to pickle fruit is that while firm fruits can take a traditional pickle brine, the softer berries often need both more acidity and more sweetness. I ended up liking these soft fruits when pickled in a sugar-vinegar gastrique, which sounds fancy but is just making a caramel sauce, deglazing it in vinegar, and then pouring that over the fruit like a brine.
Additionally, the softer berries tend to mush when canned, so I often just pour the hot pickle liquid over the fruit and then refrigerate. If you have very soft fruit, I find freezing the berries and then pouring the hot liquid over the frozen fruit helps hold the structure intact as well. There are more detailed notes in each chapter’s Preserved section.