After using 3/4" MDF for most of my previous speaker boxes, I decided it was time to try making a light weight one. If sufficiently braced, a lighter box can work as well as a heavier non-braced box. I went with 1/2" MDF. All screw holes had to be pre-drilled and the final product had bracing just about everywhere. At first, the box had a little too much air-space and adding more bracing fixed it with minimal weight.
Using fiberglass, you could make an even lighter box. But with much more effort and money involved. I hope you enjoy this entertaining project.
Here is how the box looked while test fitting the major braces and walls