Okay, this sounds really hillbilly (no offense to hillbillies, but that's what my son called it when he saw it.....) , but I turned an old car roof carrier into melon beds. With the first one, I made the mistake of drilling holes in the bottom. This year I caulked those holes and drilled into the side, about 3" up from the bottom, so it holds the water to a certain level. I put a layer of old straw on the bottom of each and then filled with a mixture of leaves and compost.
The one bed did well last year, although watering was an issue due to the holes in the bottom. This year, I added the top as a second bed and fixed the holes in the first one and they are both doing a great job. I have spaghetti squash and Connecticut pumkins in one, crenshaw melons in the other. One benefit of using these "beds" is that you can move them -- I nudged the first one out into better sun with the tractor...
I also have my horseradish now in a PVC fish container -- the bins used to store fish on ice in ships. It washed up on shore here and I saved it. It is about 2' by 3' and 24" high, very durable and has holes in the bottom. I do not expect my horsradish to escape the container, to invade in the way they did in their last bed home.
I also use large plastic pots (two, three and five gallon) for growing. I have carrots in a few, parsnips, and have also have grown potatoes in them in the past (extra cuttings that wouldn't fit in my other beds). I usually use these special planters for plants that need special soil conditions or invasives. So, for example, the carrots needed that deep, loose soil -- so I use deep pots to provide the depth I don't have in my beds.
I get the Gardener's Supply catalog (and love the company -- their service is great, if you ever have any sort of problem) and noted their extensive selection of container growing, and have taken that into consideration -- when I see a catalog, I always think "how can I do that with resources I have already?"
I have even tried "cube" mesh folding storage containers from the Dollar Tree -- the kind of organizer they sell to get your closet in order, ones that fold open to make a 12x12x12 storage cube-- as a planter, as I had a couple that weren't serving any other purpose. They did their job well for one season, but disintegrated after one season.
So, go container!!!!