More years pass, more capsules are added to the fleet. At current - I have 4. 2 indoor and 1 outdoor sued year round as well as a winter only outdoor cover.
As stated, they are not for daily use and having an interior, soft, light cover placed on first really is the final step in totally protecting vehicles. The outdoor one does get pretty dirty. Pressure washing helps but they aren't show pieces. For power the exterior ones have power supply inside unit so I've moved to this setup on interior as well using a computer APC. Just a cheap one for 50 bucks so I can run a single extension cord inside to power the fan as well as battery tender. The power draw is so low that I've been able to get almost 2 days of pressure during a power outage.
One of the interior ones holds my 95 Millenia which I consider ultra long term storage. No issues and I don't have to worry. The car is inside a capsule with an interior cover and then a harbor freight tarp over top the capsule as that garage has a window. Also helps keep it a bit clean. For whatever reason the plastic seems to just soak up dirt and grime then get that dirty sticky feeling like 1970's couch covers.
I still recommend after 20 years!!! and will keep buying them.