Cut the tabs off, and use backing strips, The strips can be round, and will support the dish better, and keep it in plane, also when making ship models, always start with the bow and stern first, the center is easier to fix, in this case, you should mount the deflector dish in place first, that will allow you to put the sides on, and do what you must to make them symmetrical. Bulkheads never hurt, unless they aren't the exact size, in that case, make a small box, and have folded tabs to that to secure the sides in question, the tabs can be positioned while the glue is setting up, and the cube acts as a central structure, some models are better served with a central rectangle down it's spine, like this one. I left out that tabs that hold it onto the rectangle, I did this in 3 minutes, but you get the idea.
Something like this: