Generally you don't see much external stowage on photos of Churchills - what there is is usually strapped to the sides of the turret or to the rear fenders. There there is, relatively speaking a lot of space inside the vehicle so it is usally the bulkier ground sheets, nets and covers that are found outside.
I reckon that crews would try to avoid materials touching the muffler - tank crews tend to be very wary of fire.
AVRE crews certainly attached ground sheets and the like to the sides of their turrets and the official stowage diagrams show a camoflauge net on one side and a rolled waterproof cover on the other
I can't say I've notice stowage on the front fenders but then these are often are damaged or missing (when you consider the drivers field of view this isn't surprising) and so its not the place to store your valuables!