I would be concerned about glass tanks outside, they can overheat easily killing your rats. Newspaper sucks as bedding, tried it once. It does not absorb the urine at all. The animals will be sitting in it and it can cause urine burns and lung issues. I buy pine bedding from a feed store where I get hay for my guinea pigs. I get two big bags of pine for the same price as one bag from a pet store. I use to feed dog food too, but recently switched to rodent blocks. Not only do the rats like the blocks more but they look healthier. Their coats are not greasy looking anymore and they have no more scabs. I know that your rats are only feeders and not going to be around long but healthy feeders makes healthy snakes. Also having the rats outside will attract wild rats and mice, which may have bugs and diseases that can be passed to your rats. If there is no way to get the rats inside, can you get a small shed set up for them. Make sure it is well vented with a fan too. Also don't be surprised if they stop breeding in the summer when it gets hot.