Make sure your turkey is completely thawed and dry.
Put the turkey in the empty (cold) fryer.
Pour enough oil to cover the turkey and a bit extra.
Pull the turkey out, set it in a pan.
Now heat your oil up and when hot, add the turkey to fry. This helps to keep you from overflowing the oil and burning your house down.
Best deep fried turkey I had was one where someone took a giant food service size can of
jalapenos in escabeche, and used an injector to suck all the vinegar-oil brine up and inject throughout the turkey. This tenderized, flavored and moisturized the meat.
Plus we got to snack on the jalapenos while we were waiting.
I've found that commercial injector marinades tend to be jars of chemical ****, and they taste appropriately. Plus the leftover meat seems to develop a funky texture when it cools.
I think a dry rub would just burn up in the fryer and contaminate the oil.