If you're trying to erect the penis of a cute dead guy, it would be easier just to inject a two part silicon based epoxy into arteries supplying the penis. The pressure of the injection would make it become erect. Then, the epoxy would set and keep it that way. I recommend a silicon based epoxy because it remains flexible when set.
If you want it very stiff, inject Gorilla Glue. It is activated by moisture and sets hard.