If it’s a pellet grill I’d do it fat cap down. Unless you can do it on the top rack with a water pan under it, then back to fat cap up. The fat cap will protect the meat from drying out from the heat source, if the heat source is directly under it.

I rubbed mine with some mustard, then a mix of brown sugar, coarse black pepper, salt, and garlic powder. Pro tip though, after the mustard put a good dose of coarse black pepper on it, and after everything is rubbed on, give it some more coarse black pepper. The coarse black pepper really helps everything catch and build a good bark.

As CeeHawk said watch a video on trimming it. I try to get mine to 200F in both the point and the flat. After about 165F or so I’ll wrap with butcher paper, put my probes in it, and throw it back in. I’ll rotate it here and there if I need to, as the point and the flat often don’t want to heat up with any sort of parity. It’s better if the point heats up to 200F because it’s so fatty it can stay there awhile, but the flat will start drying out if it stays that hot for too long.

Once it’s all done, the most important part is a good rest. I’ll usually lay it on the counter with a foil tent for 30-40 mins and let it come down a bit so it doesn’t keep cooking, then throw it in a cooler with some towels and let it stay in there a few hours. It really helps let all the juices settle back in.