"Pit" is probably a drastic choice of a word,  It really only requires about 3 inches.  If you found a crevice on a rock, that would work, too. 

Also, I forgot to mention (sorry) that your "pit" should be wide enough for some oxygen to get to the coals.  Its so obvious to any seasoned camper, I'm not sure why I forgot that important detail.  Ooops!

The biggest problem I see is digging the pit.  1) sometime there is not much soil if any.  2) Make sure you fill it in so it does not ditract from the camp site.
Otherwise sounds like an interesting solution to baking.

You'll have to let me know how it works out for you.  It shouldn't be too time consuming, though.  Most of your mixes only take around 15 minutes to bake.  Anyway, you'll impress your company when you serve cake fresh form a cardboard oven on your next camping trip!

Actually I don't know why this wouldn't work on a canoe trip, too.  Seems to me the box would fold flat easily and the whole setup would weigh very little and take up almost no room in the pack.  All you have to do is make sure the cardboard never gets soaked.  The oven bag top is a great idea too!

I may well try this one out on my next trip.  This might be just the thing to get me back into baking on my trips, something I have given up due to the weight and ineffectiveness of many of the oven options out there.  It's still kinda time-consuming (baking or fishing is a no-brainer choice for me) but it seems this idea conquers most of my other reasons to forego baking the past few years.

This is one we learned in girlscouts.  I've done this a few times since in other camping situations, but never in the BWCA.  You dig a small shallow pit just smaller than the base of your box, yet big enough to fill with a few hot coals.  Over the pit you place a cardboard box after removing the top and bottom and lining the inside with aluminum foil.  Half way up from the base, take a few wire coat hangers (straightened out) and run them across  as an oven rack.  You will have to poke holes on either side for the wires to stay in place.  You can use foil to cover the top or a turkey oven bag works great, too, it allows you to watch the food without letting heat out but it still withstands the heat.  Put your hot coals in the pit and a pan of whatever you want to bake on the rack and bake until its done!  This is great for any of your baked goods.  We once baked a delicious pinneapple upside down cake in the Black Hills.  The following night we used the oven again to make a homeade pizza.  And, just a few weeks ago, we baked a chocolate cake at a campground in Iowa!  But, I probably wouldn't recommend this for a BWCA trip with a lot of portaging.  Its probably not good for solo trips either.  But there's nothing like freshly baked goods when you've been away from civilization a few days!