Hi!
I also play sylvaneth and what I did and what i think is the best is to magnetize you models!
I got some neodym magnets from aliexpess (you have to wait a month, but 3$ for 50 pieces is awesome). I glued them with superglue under my models and I have metal box from the diy market (32x22x10
cm for 12€). I can stick them inside and they are stron enough to shake the case around and to put it upside down!
My first magents were 10x2mm but they are a bit strong, I now ordered 6*2mm ones.
Keep in mid to not glue it in the middle, so you can tilt your models to take them out (I glued them always to the side where the dryad is facing so i know in what direction I have to tilt them).
Not one model was harmed by now
you can get a bigger box, but mine is big enough to store the start collecting box, 5 tree revenants and 3 kunoth hunters!
Good luck!