I don't know how brining it first would go either. The thing about meatloaf, is that preparation is relatively simple and it's convenient for a weekday supper. If I'm going to start brining and grinding it, I may as well not bother. I got the recipe from a low fat cookbook, just to try and expand on my healthier option repertoire.
I read your posts about brining meat and I've tried your suggestion of salting well in advance of grilling, which I've found to improve the moistness and tenderness of the meat.
As for the turkey meatloaf seasonings, there's grilled onion, chopped apples (to add moisture, I guess), marjoram, parsley, garlic, sage, black pepper and salt (just 1/2 tsp). I figured that all that stuff would be sufficient to give the loaf some flavour. But, it just didn't meet expectations. I don't know if it's just a psychological thing - expecting a meatloaf to taste a certain way and when it doesn't, it seems something is lacking.
I have to be conservative with adding salt to food, because my wife has hereditary hypertension. She's not overweight and she exercises, but she still has to be mindful of it.