I ran a Chubby for half of the 2010/2011 season and had a problem similar to yours where I was unable to idle the stove lower than 300*.
Do you have the heat shield on the bottom of the stove? If not is the center bolt hole plugged? If not that could be a source of the leak. Remember the legs, heat shield and top are bolted to the stove. If the bolts are not tight they are sources for leaks. I also did the dollar bill test on my Chubby and it was tight but when I closed the ash door I could clearly see where the door was tighter on one side and loose on the other.
You could take a mallet (rubber) and tap on the ash door and see if you can get it sit tighter. Another thing you could try is a different gasket on the ash door, I ended up using a 5/8 gasket. It helped a little bit. And again, check the door pins and hinges, if the holes in the hinges are elongated and the pins are loose it could also cause the door to not sit properly. You can also try adjusting the latch on the handle. What I did was used a "C" clamp and compressed the handle a little more to make the door close tighter.
Are the gaskets still soft? If the stove sat in storage after being refurbished it may be possible the gaskets dried out and may not seal properly. You could try changing the ash door gasket. Is the hole around the shaker rod elongated? You could take the rod out of the stove and put a washer on it to seal the hole up a little more. You could even try two washers and a spring in between them to keep pressure on the washer closest to the stove.