I just put a front rack on mine, could you give some idea as to how you made yours? Or a guide you followed if you did? Is it water proof?
The bag? I made a box with k-line foamboard with the size i wanted (four sides, one bottom). Then i made a sleeve of cotton duck and also a bottom and cover. Inside i used a water proof material wich is used for outdoor covers. Everything glued with contact cement. After everything was assembled i used a leather strip to reinforce the edge. I have used it in pouring rain for hours with zero leaks. You can use whatever you want as long as the box is made of some kind of lightweight waterproof material and the inside is lined with a heavy outdoor waterproof material.The outside of the box can be anything that has some resistance to wear.
But i will replace it with a Gilles Berthoud bag when i can, it´s expensive but a really good investment.