If you are doing only one or two sheets at a time, you can develop them in a 120 tank - either singly by bending the sheet emulsion side in, or multiple sheets by slipping an elastic band around the sheet (so called taco method). I used this method when I began, and it works fine.
For most plastic tanks, you need the centre column in if you want the tank to be light tight.
I've since gotten hold of a Paterson Orbital, which is sort of like a tray with a lid on, so can be used for daylight developing. It can do four 4x5" sheets, two 5x7" or one 8x10. Very easy to load, and uses a minimal amount of chemistry. No problems with scratches or uneven development.