Always been a supporter for motorised arty. Even pulled arty. Wonder what would be the best though. But IMHO it would add a new perspective into AH, where arty would be a serious threat to both the town and the Hangars. On some maps the range from spawnpoint to the nearest target would allow a very short drive, if any at all. And our Willy's GP would have quite a job spotting!
Would the Sturmtiger fit the role? I think so. Kill a hangar with 3 shots from 4 K

But there would also be other lighter and faster that had a similar range.