Hallo,
The best is to find a big piece of trunk, cut away all the small branches. Corn does not climb that much anyway. the best is to find a piece which is band a bit and a bit longer then the length of your tank that you can rest it on the bottom and the banded part will point upward, since it is a bit longer then the tank, it will secure itself at both end. And the reason that to use a thick piece instead of a thin branches, it will hold the weight of the snake and as it grow bigger, it can also rest on it easly. Best of luck.
Here is a photo of my corn resting on his tree, well this picture only show 1/4 of the trunk. the whole piece is somewhat 52 inches