Do the bubbles stand the sharp parts? I think longer spikes will still be problem.
I put them in cardboard boxes on a layer of crumpled newspaper.
When I have to put them into boxes, I stuff some crumpled newspaper into the pots and fix them with some masking tape. So the soil stays where it should. crumbled newspaper is my favorite, form a sausage like newspaper crumple to wrap around fixes as above, works too.
Its cheap too.
Polystyrene board put on the Spikes works also well for the more sturdy ones. So the cactus holds its own box.