@teresa_arroyo Very good-looking drawings
Here when I ship artworks (rare, and only for presents) I usually put them into A4 cheap plastic protection (I don't have the exact word for the vocabulary, but they are the one used by students to put photocopies of their courses into ring binders; I just cut the part adapted to the rings). To strengthen the things, I collect cardboard sheet from packages and I put one at the back of the drawing. This way it's protected against wetness and folds.