I'll tell you what I'm doing about a similar problem with the Buck 91, but first....
A thread title like yours will always bring out several folks telling you to give up and just shovel the ashes out....too much hassle, they say. I'll admit, the ash dump isn't as good as having a grate in the floor of the stove, but to me it's a hassle to shovel 'em; You have to work at it to keep ash dust from flying everywhere (you need good technique, which you also need to use the dump effectively....shaking big coals off the shovel, etc.) Pretty sure these folks end up with more dust in the house than they would like to admit. Sometimes I want to get ash out of the way but don't want to go outside right then to get rid of them....maybe it's cold and windy out....like it's been all winter here so far!
I'd rather just go out once every couple days. I'd say give the dump a chance....try it, you might like it.
Here's the short version of my saga with the Buck 91: The ash dump leaks air around the pan gasket (pan doesn't lock in tight, just slides in.) I made the mistake of removing the high-density OEM gasket and replacing it with the cheap, leaky gasket you find at most stove stores, hardware stores etc. Do yourself a favor and pay a little more for OEM gaskets.
Yes, the lid can be held open by a coal, so make sure you push them away from where the lid seats, then close the lid. I tap mine a couple times with a poker to make sure it's seated. Then, as DuckDog mentioned, you can push some ash around the perimeter of the lid and run a shovel over it to pack it in. I'm not sure how much good this does, though.
Here's what I've been doing for the last couple of weeks and I think it's gotta be working. Not sure since I don't get to observe the full burn too often, but I've been back a couple times and the load has been burning as I expect it to.
The air wash mainly shoots air to the center of the load, and I think the left side was taking off with a combination of the air wash and the air from the dump. When I'm ready to load I shove the coals right, away from the ash dump. I'll stack a couple of splits against the left wall since the side walls are the last wood to burn. Then I'll shove the coals against those splits, over the right side of the ash dump, and proceed to load the rest of the box. My thinking is that the coals will eat up any air coming in through the ash lid and prevent the left side of the load from gassing until later in the burn. I'll even put a split on top of the coals, and it doesn't burn up too fast since the burn progresses from the center of the load out to the sides (I use the 'shot gun air' to get the center burning and the stove up to temp with a fresh load.) Another thing I've done when I've got some ash in the pan, is to put some coals on top of the pile, right under the ash lid....that may catch some of the air, too.