You can not single-box stuff that weighs 50-100lbs.
No matter how much bubble and peanuts you put in, the outer single cardboard layer will give to the weight of the item, and it will be crushed and become loose inside...and then that's when the damage happens.
I few years back I purchased a used, spare Fostex G16 from a music store up north. It was in a rack, and they were including the rack...even though I didn't want it.
They put the whole thing inside a single box...almost no bubble other than a couple of small pieces...and being that it weight well over 75 lbs with the rack...the FedEx guys probably dropped it.
It came to me with the reel motors sheared off...and the head block all smashed...since these items stuck out of the rack.
Anyway...the music store gave me full refund and paid to have it shipped back...so problem...but I mean... how stupid can they be when packing large heavy items...???