I can't install the wallet. There is no online wallet to withdraw the coins to?
There is a minexbank.
If this is what you meanby where to store them.
Minexbank wallet also needs to be downloaded. There is no online wallet which I can use without the need to install it on my machine.
Unfortunately for you, there is no any online/web-based wallet. But you should be able to withdraw your MNX into exchange wallet ( probably after August 9th).