No outer box on a Pelican case is never a problem no matter what is being shipped. Lock the case for sure, wire tie the other lock points if they exist, and it can be a good idea to tape around the lock and latches so they don't bang around and get snagged on things, as another prevention of opening AND tampering.
Tape the labels on directly, and make sure they stick well. Consider a backup external label, and always include full to/from contact info (email, phone, not just addresses) INSIDE the case, top item, first thing they see when opened, in case the exterior is damaged and they need to try to get it to you. For sensitive items, this will also mean they see paper before gun (yes, even if it's visible around it, their mindset is to find paperwork) so it will slow down their OMG A Gun reaction if that case does occur.