Thanks. If yours are already pretty much going on one end, then, yeah, you'll probably be able to get them trained without too much trouble. I have found my cage to be so easy to clean. I've had other types of cages (NIC, etc) but have found this one to be the easiest.
The 'oven cabinet' is just a kitchen cabinet that is made so that an oven can be inserted into it. My husband does kitchen remodels, so that's how we got it. Making the cage was a fun project. Since we already had some materials on hand, it only cost about $25.
And, yes, mine are indoors. It is rare they go outside since we live in the desert and it is just too hot most of the year. We're still having daytime highs around 90F here in mid-October.
If you ever get the chance to take photos, I'd still like to see how that works with your cage and the shed and outdoor pen. Sounds like an interesting set up.