Hi Kevin, sorry for not getting back to you, I was tied up with work. Thanks Don for your reply's 100% correct with the ceramic wool. I can get it from a local place that works on industrial furnaces, they also sell firebrick but it shouldn't be to difficult to find it online. It may be marketed under the trade name "Koawool". People use if all the time for propane forges etc.
As Don has stated the ceramic blanket is dense enough to stay put if sized slightly larger and crammed in. After a few firings the tars etc of the wood seem to "bake" onto the outer surface making it rock hard and no chance of falling into the tube. As a side there are coatings you can buy to parge the surface to add protection and thermal properties to the ceramic blanket. I have no experience with these but have found "virgin" ceramic to be performing and holding up very nicely and these coatings are quite expensive.
my heated hopper is as follows:
gas exiting the grate is run into a cyclone filter which is then channeled into a jacket that surrounds the entire hopper which then is run into traditional cooling rails.
a more ideal setup would have the hot gas run THROUGH not AROUND the hopper fuel but so far the current system is running well. I have not investigated how wet of wood I can use but do see alot of condensate being collected with any wood that I use.
Others have posted "through" heated hopper ideas on this or other threads (like Chris S) but there does not seem to be any "easy/fast" ways to accomplish this. The "around" hopper was fairly easy to make however it was very time consuming (3-4x as much as the firetube) and difficult to check for leaks and I will have no way to make reliable repairs to it once its service life is up. On future gasifiers I will be pursuing a "through" heated hopper.
All the best in your endeavors and I'm happy to answer any questions you have but I don't want to distract from Dons original thread subject