Packaging

How do I send a canvas in the post? I have wrapped it in bubble wrap but when I got to the post office they didn’t have any boxes big enough. They suggested I put it in a bin liner and tape it well but I didn’t think that would be secure enough. I asked them if they had any old cardboard boxes and they gave me two small boxes with low sides. I will try and unfold them and use them to strengthen the front and back. I was then going to use a black bin bag, but I went in the petrol station to fill up. They were chucking out a large cardboard box so I asked for it. I will use that as outer packaging with lots of tape. I’m glad I called in. Wish me luck, and the canvas a safe journey X.