Pork Loin is lean. So you want to cook it no more than 145 so it doesn't dry out. Or you can brine it which will make it more moist. I don't think marinades are that good for a thick cut like this. They don't penetrate much so I think Loins are also a good candidate for injection which is much quicker than a marinade.
They also lend themselves to cutting in a long continuous sheet, filling, re-rolling and tying for cooking.
Indirect heat on a grill with a finish over high direct flame to sear and color is very good, especially with some hard wood chunks for a little smoke.
Loins are easily cut into chops, but they should also be cooked quickly and not past medium so they don't dry out--see above, but chops are good candidates for marinades.
One of my favorite injections/marinades is as follows:
3 cloves garlic, minced
A single Fresh herb, about a tablespoon chopped--rosemary, oregano, or thyme and a bit of sage is the only one I would combine for this.
olive oil, about 4 tablespoons
juice of two lemons, zest too if you're so inclined, but that can be a bit strong
about 1/4 cup white wine or apple juice
1-2 tablespoons dijon mustard.
salt and pepper to taste
whisk for a marinade, Blend well for injection, though for injection its best to make this an hour or so ahead, then strain out the garlic and herb chunks as they tend to clog injectors. Save the chunks and rub them on the outside of the roast.
Also very good on chicken, this marinade is excellent for grilled foods and good for other cooking methods.