RE: how to sttrengthen without adding weight?
Ameyam , before you get torn apart quicker then your airfram lol , its really about what you are comfortable with .
You aksed a simple honest question that many of us can not answer because the typical 3D plane structure looks nothing like most planes , in fact I spend most of my time in the warbirds thread and many warbirds are on avg heavier in wing loading then the typical bird.
To accomplish what you want -stregnth and light follow the points so far .
1)CA will soak into the frame as seen in the pics
2)carbon fiber tape is good , some can be heavy
3)Flight skin is great if cut to size (in strips in your case ) and ca in place .
In closing if you want to nail down your plan and move on , state the current wing loading , that will give most guys who know 3D a idea if your current wing loading is low , mid or high and you can then determine your margin of error .