I have only the 18-55mm f/3.5-5.6 IS kit lens on my Canon 450D though I have rented other lenses. There is a lot of sound advice on this thread.
I have used my 450D and kit lens in the rain, hiking through the woods, kayaking/canoeing, and mountain climbing. It has been bashed against rocks, dropped, and rained on. I always try to avoid this, but a little abuse is inevitable. I have never had a problem.
That being said, you will really need a 300-400mm lens to adequately take pictures of wildlife and you can not afford one at this point. Consider renting a lens when you know you will be spending a lot of time in search of wildlife. I have rented the 100-400mm f/4.5-5.6 three times now and I plan to buy one when I have the money. Right now, I am in the same boat as you. I can't afford it.
For rentals, I have only used Lensrentals.com and I have always gotten great service. I would definitely recommend them.