Very hard than you can imagine. Haven't you heard of memory lose before? Brain dimentia and so on? Yes, we all know the danger of writing seed phrases on a tangible materials but cramming it is not the best way neither. Writing on a paper should be out of options completely as it is not secure at all. In my opinion, metal plate has covered me and my seed phrase already.

Look for a sizeable flat metal plate, a nail or needle and hammer to print your seed phrases on the metal by making it in form of hole. It actually takes a little bit time but it is more safer and resistant to both fire and water. Ensure to save it in a dry, clean and private place to avoid hole blockage.