Officially, it is not known to be rust-proof. If you keep any of these toys out in the elements all-season or for months on end, they are probably bound to develop some rust. That said, we recommend that once playtime has ended outdoors that the tonka trucks be brought inside.
These are items are also pretty easy to clean-off, air out and dry to prevent rust. Also, there are many water and rust-proofing treatments you can use. When all else fails, Tonka offers a lifetime warranty that any parent can fall back on if necessary.