You don't need to do a messy, one off spray foam job with CRT's.
Home Depot sells their own brand of large pile bubble wrap that is orange in color. It's about $35 for a 2 foot wide by 100 foot long roll. Thats what I use it it's great.
Packing standards (when it comes to insurance) caalls for 2" of spoace between the item & the box interior on all 6 sides. That is for normal items that are sold at retail today. CRT's are more of a specialty cataory & you want to go with 4 to 6 inches on all 6 sides (4" for small and/or lighter CRT's). Large pile bubble wrap for the first 2 to 3 inches & then a stiffer foam for the rest. Pooly styreme is O.KJ. but brittle. I forget the name of the other (much better) foam that I use but I will get a pic.
The problem with straight foam jobs like Poly & spray foam is that the former breaks on impact while the later has more give but is less resilient. Plus both are too stiff when it comes to a parcel getting hit with blunt force. The bubble wrap gives older electronics just a bit of needed wiggle rooom & is better with absorbing some of the extra inertia.
It's not just about the dangers of a CRT getting damaged by something outside in post but the CRT damaging itself in the post. This goes double for flat CRT's, Trinitrons & those with plastic cabinets with plastics that have aged worse over the decades (white & off white castings, etc).