For sure, my man. I actually got the idea from the salt water aquarium guys, and you know they don't mess around when it comes to luxurious reefs.
I only use one o-ring per bulkhead, on the outside of the containers. (size 331 for 2 inch fittings)
The red silicone ones are the best.. Feels like it gets a better seal IMO, but the regular rubber type ones work fine, and are cheaper. I torque 'em down good with big daddy channel locks.
Either way, I been DIWHYing bulkheads like that for years now, and never had a problem. Made many different systems with them, using all different sizes. Never a single leak, on any connection. Solid.
No sealant needed (Not that it isn't good to always have some around). I always use square buckets/containers with a flat surface.
I wouldn't even try it on a round bucket. Well I have before.. flattened down the sides of the buckets, using blocks, clothes irons, and parchment paper to reform it.
Much easier to get square buckets now days, especially at L0w3s.