I am building a new cage for my guinea pigs. Its going to be a 2-story cage with fleece flippers. Since I can't cut a hole in the middle of a flipper, we are going to make the ramp a PVC tube that goes out one end of the cage and goes up at an angle to the top. This way they can walk right out on to the fleece.. IS this safe enough? IS there any other way to do this?