So your hastely constructed cover is so good that it blocks line of sight and is still mobile?Getting PCs to leave the safety of the hut is kind of the point. In the group I'm currently running we have only 1 wizard with AOE spells. There's a cleric too, but most of his spells require line of sight.
And what does making the party leave the hut achieve? Nothing unless you, besides carrying around the supercover you also have hobgoblins ready action to shoot everyone coming out the hut for up to 8 hours. But to do that they need line of sight themselves, so cant be protected be the supercover and can be sniped easily.