I agree with this. I have not seen any medieval tent design where the floor was an integral part of the tent. And only the smaller tents have integral walls; any large tent has seperate walls, usually in several sections.
To me, the spells cast at the backpack and the hut remain in effect. I would also support adding a Target: Container option, with some sort of size limit (linked to the Form of the effect?) being +1 magnitude (instead of +2 for Room).