Yeah, that trick with the welding blanket is solid. I've used one on my old offset for a few years now when it gets windy. It's not pretty, but it really does help hold temp without spending a lot. Just make sure it's fiberglass, not the kind with a rubber backing.
Totally agree on the fiberglass thing, that rubber backing would melt right off. I threw an old welding blanket over my cheap offset last winter during a cook, and it was a total game changer. The wind was howling but my temp barely moved for hours. Ugly as sin, but who cares when the ribs turn out that good.