For boxes for shipping paintings I use a company called Airfloat. Their boxes are puncture proof, and make packing a painting very easy. Although to my knowledge they don't have boxes for 7 foot paintings, they do have boxes that handle paintings up to 5 feet. Their website is http://www.airfloatsys.com/.
Fed Ex is the shipper that I use. I've never had a problem with them.
Hybrid Mode
