Isn't straw supposed to be quite good for holding heat?
Straw is good, hay is too. I use hay in the outside kennel I've got for the two neighbour's cats who are left out in all weather. I've got vinyl on the floor of the kennel, topped with vetbed, and then that is topped with hay, literally packed in to the rafters lol! You can see where the two cats have sort of burrowed in and there are 2 little indentations left where they sleep
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I don't really know about temps, only what it says in my boarding cattery manual, that 'the ambient air the cat breathes in must be within a range of 15-26 deg C, despite external temperature' - but of course thats talking about a cattery situation. If you get a maximum and minimum thermometer that will tell you the highest and lowest temps measured.
Worming granulues I only know Panacur - but think they are only for 1 type of worm, not both?