A lot off people including mobile detailers buy sturdy pop up gazebos with sides for polishing outside. Like me if you have no other option it's doable, even if you only do a couple of panels at a time. It's not cheap to get into as you can spend as nearly as much on pads and compound/polish as the machine itself. My sister inlaw has an mx5 and I had a quick play on the boot lid, it's black and it came up lovely after very little work being soft Jap paint. There are some very good glazes out there which will hide the swirls but not scratches, 50cal filler glaze, KKD regloss, Poorboys
Black hole and more. You could always look for a second hand machine, many buy try and quickly sell on.