How much time and how much money are you willing to spend on this, and do you want to reuse it again for another con or event?
Given my own time, craftiness, and budget, I’d want to make something light and re-usable, and only involving one prop for me to manage.
Go to Michaels or Hobby Lobby or JoAnns and get one of those really big oversized paper-craft boxes that look like books, a square of foam that’s slightly less thick than the depth of the inside of the book-box, a stick of inch-wide and very thin balsa wood, and some fabric or felt to cover the inside of the box with the foam in it, and to cover the inside of the lid. If it were me I’d get fabric that looks like printed or manuscript words but I’m a perfectionist and an overachiever.
Foam goes in box, fabric or felt goes over foam and on the inside of the lid.
Make sure there’s still about half an inch or 3/4 inch of depth remaining in the box between the top of the foam and the closed lid with the fabric/felt lining.
Take your poster board and do some measuring. You’re making a one-page pop-up book here. Your Rainbow and words are gonna need to be a little bigger than the book and so you’ll need to work out how far out to the sides you can get without being too floppy. As a wild guess I’m gonna say 3 or 4 inches max per side.
So you’ve got the width of the open book, plus about 8 inches total. Paint your rainbow and print your logo to fit in that set of dimensions, then draw ‘tabs’ like on paper dolls on the bottom on either side of the middle about two inches or so away from the centerline, and then again just inside the sections on the sides where it will overlap the edges of the book box.
Now cut out your shape and remember to leave the tabs!
Now go to YouTube and follow the directions for making a pop-up page and attaching it to a base in a book, cause I can’t explain that in writing and have it make sense.
Voila! Light, portable, folds up for travel or panels or lunch, and looks complicated as hell but really isn’t that hard.