This is how I make my own boxes to ship my artwork. By making it to size you are cutting down on weight and dimensions which is great for the shipping cost
Shipping Paintings - how I build custom boxes
How to Safely and Securely Package Your Artwork for Shipping
16way trophy
How To Make Decorative Storage Boxes Using Gel Press Plates
Sun Path HQ
Art Shipping Boxes, Artwork Boxes For Shipping
This Cardboard Box Hack Will Help You Pack Longer Items
How to create professional custom packaging to ship art!
DUBAI 500 Euro Captains16/32 way
How to Safely Package Your Art for Shipping - How to Sell Art