I can answer the last one - about the only thing that is going to keep a uke from cracking further is keeping it humidified! Beyond that, merely the obvious, don't leave it in your car in hot (or very cold) weather - avoid sudden drastic changes in temperature. For example, if you've been traveling and you uke is very, very cold, do not open the case for an hour or so after entering a warm house.
YOu don't mention what kind of uke. There are some kind of "off-brand" ukes that were made with solid wood but the wood wasn't properly seasoned - those will almost always crack and there isn't much you can do about it but maybe keeping it really, really, well humidified.
On the other hand, "warped" sounds almost like it may have been water damaged?
Hard to give a meaningful answer without pictures...
John