Corner brace for 15x15mm square tubes

I couldn't find a square corner brace for 15x15 AL tubes (or wood if you want) to make an enclosure for my Ender and also for a growbox to grow chillies.
I really liked the 45°printing angle that I saw in a video somewhere and couldn't find it. 
Probably will add braces to mount it to the surface. so a 90° single tube mount or if requested more different braces.

I hope you like the model