Evening Hmm,
I have the same Costco one with the stainless cover.. thats the one I use for bbq'ing when i go camping. I actually like it alot.
Where the propane bottle goes in theres that small galvanized pipe with two airholes on it, when the propane is shot in, it flys by that hole and sucks in air. try covering one of the holes a bit, dont completely block it.. then you will not get enough air. Block the hole partly will give it more fuel to air ratio. I know what you mean about the holes being too big.. i noticed that as well.
Now you have me curious.. when I get home Ill do the bbq then oven method using my camping bbq. <sigh>. two more weeks!