I'm not sure if these are available elsewhere, but I made these to allow me to easily clamp boards, such as foam boards and hardboard, even cardboard, together into a box shape.
For each corner, you'll need to print 2. Run a nut and bolt through the hole, and you're off.
I will use them to build a foam box enclosure for my I3+, as opposed to buying a table from Ikea.
I added an elevated part. This was because I wanted to lift the enclosure up a little, to allow some heat to escape, as the main printer body, and electronics, were getting too hot. This alleviated the problem.