From the above link, two models were used-
"Missing no detail less the "We brake for nobody" sign, the featured 40" x 8" x 4" Spaceball One prop was used in tandem with a ginormous 17' version to depict the impossibly large ship, which allegedly houses a shopping mall, a zoo, and a three-ring circus, and takes about 1:43 to cross the screen in the above video. The smaller model appears in Spaceballs wide shots, where it appears way over yonder, or is shown blasting away from the camera."