So if you are trying to design an IP67 seal on that part, I do not see you getting away without a custom seal or custom O-ring.
To build an O ring seal, you need to create a channel around the perimeter of the product (Which will add ~1.5X to your wall thickness dimensions since you will need an inner wall, channel, and outer wall). You then need to create the opposite profile on the other side of the part to compress the O-ring.
You also need to determine how whatever happens on that bottom piece will get sealed, as well as how your screw bosses will get sealed (Ideally you want your screws outside of the sealed area so they don’t create additional entry points).
More important to consider is “What” are you sealing. If you have electronics inside, you may be able to just seal the PCB’s with a simple box enclosure and a square seal vs trying to seal the entire perimeter of the product.
You could also Two shot one of the housings and add an elastomer/TPE shot to one part that creates the seal as part of the housing which then gets crushed on assembly. It makes for 1 more expensive tool, but the cost might be cheaper than creating an additional seal.
Probably a lot of ways to tackle it, but I think either way you’re not going to get away with a simple off the shelf O-ring.