You're making this far too hard. The drum you have is the same diameter as a 18.5" weber kettle.
Find an old 18 kettle on craigslist or a yardsale. Part it out. The lid will fit perfectly on top of your drum. The charcoal grate is the perfect size to make your charcoal basket. Wrap the outer edge of charcoal grate with a 6" high strip of expanded metal available at lowe's. Connect a pizza pan on bottom of charcoal basket so when you lift the whole unit out of the drum, all the ashes come out with the basket, like this
That's for a 22.5" UDS, but the principle is the same. The cooking grate from your donor kettle is perfect size for your 30 gallon drum. Buy one more "cooking grate" for a 18" weber kettle", and you'll be set. No silicon, , hinges, latches, access door, no one off coal basket that doesn't even fit into the drum.
You don't need a farking access door to add fuel or wood. Leave the drum whole, the fire basket is loaded with unlit charcoal and wood, dropped into the UDS, then either lit with a torch, or a dozenish briquettes are lit in a chimney, then poured onto the top of the full basket. That right there will get you 14+ hours of cooking. No reason to have latches hinges, etc.
