A few things:

When I was shooting with the Sun 600, I found that the black bags that my Ilford 5x7 paper comes in fit snugly over the ejection slot. The picture ejected right into the bag, never seeing light.

With my Spectra which is too large for that, there's a hand feature whereby the picture won't eject until you release the shutter button. Press and hold to take the picture and let up when you're ready to eject. As mentioned, I keep a dark slide with me and allow the picture to eject against it. Then I bag it. Don't know if your SX-70 works this way, but the dark slide trick should still work. You just have to be quick about it.

I'll order the Color Protection when they release it for the Spectra -- some time this month allegedly. I've heard nothing but good about it.