How to setup a custom screen post processor with multiple passes.

I'm trying to do my own custom shader for a blur which I then just add to a camera as a component. First blur pixels horizontally and then vertically (2 passes). But I can't seem to find any documentation for how to achieve making your own RenderTargets to read in and out of for a shader. Essentially I want to setup a ping pong for 2 framebuffers and then spit out the result.