Baking Turkey Meatloaf with/out glass cover
Putting the lid on will tend to steam your meatloaf on top, rather than baking it, as the moisture that evaporates from it will have no where to go.   This will inhibit getting those nice crispy brown bits.

If I were to double a meatloaf, I would not simply put it in a larger casserole.   Instead, I would make two... erm... loaves.  This would:


Ensure that they cook at approximately the same and expected rate, as predicted by the recipe
Provide more surface area for the delicious brown bits.