Good call noting that you tend to store fat easily. For people like that, insulin can ruin a physique fast. So I would be very careful moving ahead with it and I think you are on the right path, maybe just using it on specific workouts for weaker body parts. Also remember you don't have to use high doses to get good results. You have to take enough carbs to cover the insulin but as long as you are getting 50-60g carbs a meal, 5iu with your post training meal would be a god place to start and see how you’re responding. Try this on just your weak body part days and then after a few wks, compare pics and weight and see what you think. Ease your way in. No need to go too high too fast, especially with your body type. If you are using gh through the process, that will help to ensure you stay a little leaner. At 39, you’re at the age where GH will start to make a nice difference even at moderate dosing of 3-4iu. The only downside to this plan is that you could still get fat haha. But if you take your time and watch your progress you can do well. Keep the carbs clean and match your insulin to your food, not your food to your insulin