Will these sample tubes stay on the rover itself? Or will they be put on the surface of Mars? This latter way does not make sense to me. Squirrel effect: how could a future rover find them? Storms on Mars will cover them with sand ...
Will these sample tubes stay on the rover itself?
No. There is no facility for storing all 43 sample tubes on Perseverance.
Or will they be put on the floor of Mars?
Yes. The sample tubes will be "cached" on the surface of Mars, either individually or in small groups. 3 have already been cached.
how a future rover could find them?
It doesn't need to find them, since NASA knows exactly where they dropped them.
Storms on Mars will cover them with sand
NASA has had the exact opposite experience: Spirit and Opportunity were only supposed to last for 90 days until their solar panels are covered in too much dust to generate enough power. In fact, they lasted almost 8 years and almost 15 years due to so-called "cleaning events" where wind cleans the surface of dust.