A huuuuge tub – I have a BIG flower pot which I fill only a third with earth and they love it
(if you put more earth in, it will fly everywhere !!)
Where are you ? If in UK there are of course foxes (and elsewhere other than UK of course) and they (and minks and goodness what other determined predator)are able to get in metal runs that are not fixed at the bottom, so although slabs are OK for the metal run to sit on, a fox would be able to lift it up and get his head under… and in he will be
So fixing down the entire base of the wooden run is paramount to her safety if she is using it without constant supevision, however heavy you think it is that a ‘little’ fox/mink wouldn’t be able to get under – oh yes he could…
I don’t think wooden chips are ideal, not comfy for paws I’d imagine and they will fly everywhere with Flo boinging about…
Not sure what to advise though….
Slabs inside the completely 360° sealed run…..?? (Hardly practical Vienna!
)
I would absolutely close the run off at night and keep bun inside the shed overnight…. so making a cat flap that can be SECURELY shut at night should be on your plans 