Correct, closed drum is sealed. If you buy a new one you can get unlined like I did. It has a coat of oil to keep from rusting. When I bought mine I bought the heavier gauge one. I would buy a lever lock lid instead of the bolt type I got. I got a 85 gallon drum from Grillman40 that mistakingly got sent to his work. It is 26" dia. vs. 22.5" on a 55. I had to hunt for grills. i lucked out and found a BBq and extra grills. If I had not lucked out it would be costly to get them. 22.5" weber grills are @$15. Inexpensive replacements are @ $8-$10. Here is my 85 build
Pm me if you need info. Also have powerpoint of UDS build if you send e-mail address.