Well, if you look at other weapons with no AP, they tend to either be very weak, or not the typical means of injuring someone, such as Tesla Blasters. In fact, if it was an electrical charge, like a Mechanicus arc caster but made into shell form, that would be quite interesting, as well as explain the non-typical method. The Corroder and Disintegrator wouldn't really work as it stands currently, and you might have to adjust the way it works a bit more with a unique special rule concerning how it deals with wounds or something, but it would be a very interesting way to do it, and it would more or less fit in as it's own special weapon system. Maybe, instead of getting more shots, necessarily(some could, but maybe they couldn't all go on a single model), since this seems like a single-shot weapon, the larger versions get different template options, or can choose which direction the template faces when it hits, along with some small Str increases, Haywire on a version or two(or all, since it'd only hit the vehicle per actual hit, really). The most powerful version might just be Str 6 or 7, but get a lot of shots, with the special rule that each additional hit past the first can be centered on the fat part of the template of where the last hit was, in the direction you choose (but of course the fat part of the new template can't be closer to the thin part of the old template than the thin part of the new template(yes I know that was confusing, basically think of it like how torrent currently works ish).