Take a 2 litre plastic bottle filled with water that has been frozen overnight and put it in your rabbits' cage when the temperature reaches 80 degrees or hotter. It will drop the air temperature around the rabbit considerably. Keep an extra on hand to use while one is re-freezing.
Attach a drip irrigation hose to the top edge of the hutch roof. The water running drown the back of the cage will act as a swamp cooler.
You can attach a misting system near or over the cage.
If you use a fan, direct the air OVER or UNDER the cage. NOT DIRECTLY ON THE RABBIT.
Rabbits have a very keen sense of smell and are usually sensitive to the smell of smoke, perfume and fabric softeners. Many are allergic to perfumes and dust.
Although rabbits are very clean and seldom need a bath any flea shampoo or spray that is safe for kittens is safe for rabbits. But be sure to dry the fur completely so the bunny doesn't catch cold.
