There probably aren't too many of you in the Baltimore, Maryland, area, but if you are and need double-walled polycarbonate greenhouse panels, I'd recommend Maryland Plants & Supplies. They're in the Rosedale area,
1-800-248-2818.I had special ordered some 4' X 12' panels which didn't arrive in this week's shipment as planned. I told them I needed to get the roof on the greenhouse this weekend so they substituted 6' X 12' panels at no extra cost. Also, they cut each one down to a 2' wide and a 4' wide piece so that I could fit them into my truck. Extra materials and extra work at no extra charge. I'll probably never need polycarbonate panels again but I thought I'd pass this on to anyone in the area who does.
Paul