I think smoking is the wrong way to cook this cut. I needs a good searing temp. If one wants to smoke, pick a cut that needs the low temperature that smoke requires. Smoking temps need, repeat Need to be less than 250 degrees and that is too high for the whole thing.
In short , the Porterhouse is not suited to slow smoking. Maybe somebody can tell us how to smoke quickly, It won't be me 'cause I don't know how.
If I were to try though I'dtry mesquite as I read some years ago that it was only good for fast grilling, I honestly do not know.
May you eat well,