Like I said earlier, I clean mine once a week but that is just dry ashes. Takes 15 minutes to brush out the tubes, scoop out the bottom chamber and the burn chamber. I did have more of a creosote issue building up in the tubes earlier in the year, but I believe this was due to lots of idling because of warmer weather. I was worried about how I was going to keep the tubes clean, but once winter hit, the creosote dried up and flaked out of the tubes.
I think if any of these units idles a lot due to warm weather they are going to have buildup issues. I see this whenever we have a few days of warmer weather. When the overnight temperatures start dropping to -20 and colder, the unit really comes into its own. I don't think that oversizing is a good idea with these gassers. I'm starting to really believe that right-sizing or storage is the way to go to get good clean burns and minimize creosote buildup. I think a 12 hour load is about right.
If you are getting tubes plugged up I would suspect that you are having far too much idle time and not enough burn time to run cleanly, regardless of how dry your wood is.
My wood is not the driest it could be, but it still burns fairly cleanly if the heat load is high enough. I have also found that if the wood is too dry and split too small, it will burn dirty as well as it chokes itself and doesn't gassify correctly. It can't get enough air to burn all of the gasses coming off of the wood.
It's taken me a few months, but I think I'm starting to figure it out.