When packing, put the parts in bubble wrap and place the parts on top of the frame. Then it is hard to distinguish the trigger frame from the others parts. I have never had any problems with sending paintball markers anywhere ... except Germany, North Korea.
Posted an x-mag (most gun-looking electro out there that isn't milsim) to going-home in Florida by ParcelForce who subbed it to FedEx.
It was insured and tracked and guaranteed delivery time.
I put a full description of components and a summary as disassembled. Worth including a comment about no compressed gas or batteries in package. No batteries I didn't know about until I reseached.
I posted one via parcel force about a week ago, international priority, with the contents description as 'paintball marker' and got there in 4 days with no issue....