If you take care of these things you should be safe. The real question is where are you from where paperwork packages get ripped open? You are aware that you can send in some serious complains about that and well, also definitely should do that?
This happens a lot with post from the UK to mainland Europe. Normally one corner will be ripped open but it only happens to things that look like bundles of paper from the outside. Small letters or big parcels never seem to get touched. A couple of times I've seen what looks like notes written near the torn opening saying something like 'letters' or 'paperwork' always in English. I know the people sending this stuff and it's not in their writing so I guess this is the UK borders people checking for money. There really isn't anyone to complain to about this. All the parties involved will deny everything and claim it's accidental damage.
If you stuff a few fifties inside a book you will probably be fine but you will never be able to prove a sender shafted you unless you use a non-anonymous tracking service.
I'm from Germany and over here it has serious consequences if it becomes revealed that a postman does open the letters. He will lose his job for sure and get a rather high amercement.
But yes it is always recommended to use non-anonymous tracking services for money shipments anyways.
