Interested to see this. I have done tons of research about building an expedition style box similar to how you are building this. Finishing the glass will be a lot of work but I believe it will be a very nice style.
The wings definitely need a significant amount of reinforcement. A diagonal brace on the underside as big as you can make it will help.
Are you using regular fiberglass resin or epoxy? Epoxy will add significant strength but a lot of cost as well.
As mentioned above, look into different fiberglass weaves. 1708 biaxial and woven roving are much stronger than CSM. You can find some strength charts for comparison. Direction of the weave, and using it correctly, will add strength as well. In fiberglass there are many little things you can do to make the build stronger without necessarily adding cost. Technique is important. S-glass versus others is worth comparing as well.
West Systems has tons of free info.
Excellent free resource.
https://www.westsystem.com/wp-content/uploads/GougeonBook-061205-1.pdf
Couple of very good books.
Fiberglass Boat Building for Amateurs
The Elements of Boat Strength: For Builders, Designers, and Owners