>>10618982im really surprised those are warping like that. Do you have a lot of moisture in your room, OP?
They also make similar ones that they slide up and down on like
>>10619308 has but i can't say for sure if they'd prevent warping like you have.
They do have plastic blister proector things you can put hot wheels in and then display those on a wall. I have a set of Nintendo cars in one, but i also do have single cars just hanging on the wall (being held up by a pushpin)