If I remember correctly a Slingshot is registered as a motorcycle in Illinois, so using it for the tube frame argument may not help since motorcycles have different rules. But there are many Lotus 7 replicas registered that are tube frames in Illinois - along with Cobras and many other kit cars. These are all tube frames, as we know, but the tubes are not exposed - except the rollbar/cage. The hang up could be the exposed tubes and the exposed 'gap' above the standard side panels and possibly exposed tubes at the rearend. If these are covered, the way Karter had to do his car, it may make all the difference when attempting to get licensed. I'm not saying by doing this will change anything, it is Illinois after all, but asking someone if this is a requirement might be a next step.