I\'m looking for a way to serialize a bunch of C++ structs in the most convenient way so that the serialization is portable across C++ and Java (at a minimum) and across 32bit/6
Why haven't you chosen XML, as this perfectly suits your demand. Both C++ and Java allow for an easy implementation.
Furthermore, I doubt your idea of storing everything as a blob in the database, use a relational database what a database has been designed for, or switch to some object oriented database like http://www.versant.com/en_US/products/objectdatabase which supports both Java and C++.