Some folks have used a tire for both wasters and blunts. I think the wrapping the pell in some sort of foam is far superior to using a tire that will mark up the waster and bounce back on you. Like many things, there is much disagreement about statements like that.
I have used one of those water filled base punching bags as a pell, but since the plastic sleeve on the inside of the bag comes right up to top I can't strike straight down without risking breaking the bag. My waster beats the stuffing up more than kicks and punches, so I don't use it much. I still want to use it to kick on.
I'm very new at this, but I would say that using something that moves just a bit is better than using something buried. It gives you a better feel for the power you are delivering into the blow. Something that is hanging also makes you get used to a moving target. I'm not sure if there are hanging or freestanding pells in any source literature, so a static pole with padding is probably more period.
Everyone pretty much seems to make up their own designs within a rather general conceptual framework. But you're right, don't use a waster on bare wood lest you provide the waster makers kids a better education or new shoes.
