Your tub is not deep enough to be a container but could function as a big saucer for several pots or for starting seedlings in small pots before planting out. Use any good seeding/container mix, try to get the kind that includes water retention granules. You could keep an inch or two of water in the tub so the pots stay moist.

For permanent planting, you need a container 18" to 24" in diameter and at least 24" deep for each plant. If it gets below freezing in the winter, you will need to protect the pots from freezing solid.

Given the number of plants you intend to grow, have you thought about building a bog garden? Dig a 3ft deep trench, line with plastic and fill with a mix of sand and peat moss or sphagnum moss. Allow about 2 sq ft per plant when planning the size. Detailed instructions in the link below.

Here is a link that might be useful: Buld a bog