2002 Toyota 4Runner Tire wear on rear wheels

I have a 2002 4runner with about 70k miles. I bought this vehicle about 2 years ago with about 45k miles. After owning it for a few months, I noticed it was hydro planing on wet roads a lot and would slide around a lot on wet leaves(This happened when driving safe speeds for the conditions). And when we had our first snowfall, the car handled absolutely horrible (in 4wd). I finally examined the tires and noticed the inner part of the tires were really worn, in the front and rear. The outside of the tires looked almost new. I managed through the winter with these tires and purchase new tires and had a alignment done in the spring. The tire shop told me the inner tire wear was because the car was out of alignment. With the new tires, I still have a lot of inner tire wear to the rear tires (I've rotated the tires per manufactured specs every 3-4 months. And when looking from behind the car, it has a negative camber. Is this possible with a solid rear axle? Please help. Thanks.