Dragon form should not have trample
In general, player trample is a disadvantage. When you're fighting a monster you're usually on the same side of them as your escape route, so attacking is moving you further away and putting you in more danger. I suppose trample could be useful if you are surrounded, but dragon form's defenses are so horrible that if you're surrounded you're probably going to die anyway.
Thus I think trample should be removed from dragon form. The spell isn't really that powerful so it doesn't need such an awkward and annoying drawback. Several monster dragons don't trample anyway.