there’s only 2 “missable” red chests, 1 on Athenas that requires you to collect pickled ratch livers in the Holy Distillery for that…um…“peaceful” monk that runs it. and the one behind Marcus’ vending machine in the Droughts, that requires you to bring him a human spine. (on repeated playthroughs you can miss the red chest in Covenant’s Pass, but you should have opened it on the 1st playthrough when Claptrap has you search for a shield.)
And in the Handsome Jackpot dlc, red chests currently don’t count toward map completion. (so you can definitely miss a few) I know I missed the one under the Clapstructor’s reinforced beam on my first run through there. but again doesn’t count toward map completion and there aren’t any permanently gated chests in the DLC aside from the ones that Timothy reveals with his winning hand as soon as you meet him (which is locked after that point and can only be opened once), but typically you should collect that normally during the DLC story.