My opinion is that guinea pigs can be kept indoors and outdoors.
I had four guinea pigs and have now got two who are almost 6 years old and have lived in an large OUTDOOR hutch their whole lives.
The cage is perfectly safe and it is under our back veranda.
I also Knew a girl who kept her guinea pigs outside and guess how long they lived, 8 whole years!!!
So what I'm trying to say is what is wrong with keeping cavys outside?