Silnyl is very thin. You would need to start with a very low temperature and raise it gradually until you get the results you want without the results you don't want. I sus pect it would be faster and easier to learn to roll the hems and fold the seams rather than try to iron it.
The other problem is nylon in any form is not a good crease holding fabric. There is a reason they call synthetic clothing "permanent press". I find trying iron nylon to be more trouble than it is worth.