Um, George, that's not entirely correct. Many of the western states (even those that do not allow other Class III items) do allow the use of suppressors. They are fairly common with the exception of CA.
A sleeve can be made of the foam rubber used for insulating water pipes. It is inexpensive, and should not melt too the "can" unless you are shooting a lot. It would be fine for the one or two shots normal in a hunt.
Another way to cover the suppressor would be to use a piece of automobile radiator hose. cut it to length, slice it the long way, and then just slip it over the can.
Both of those are very cheap, durable methods. I prefer the hose because of its lower profile but both will work.