Hi THrunner and welcome!
I don't have any CAD drawings - I basically started with the existing panels and then either copied them or modified the shape to fit what I wanted. A few notes though:
1) You will notice that the wall between the stove and the fridge (and also the wall between the sink and the shower) are plywood, not MDF like most of the others. These are somewhat important walls for keeping the shape of the rig (walls not bowing, overhead not sagging). They would be called "bulkheads" in a boat. Now to be sure, Chinook didn't make these as structural as they could be (they would be more securely affixed to the outer fiberglass in a boat, say), but they do something. So, as when remodeling a house, they don't necessarily need to stay the same, but their function (IMO) should be kept, whether by the original means or different means. It could even be improved upon.
2) This is probably obvious, but the reason the refrigerator is not on the floor is that beneath it is the generator box, which lives partly above the floor and partly below it. There is a little bit of extra room between the top of it and the fridge because they have thick padding and "shaggy" carpet there, but we're talking inches not feet.
3) If you are changing to a compressor refrigerator (vs. an absorption/propane one), then you won't need the sealed off chimney (since you aren't burning a fire back there any more), but you of course do need some ventilation. But there are more choices (keep the same, modify, vent internally, etc.). But be aware that there is a "differently shaped" part of the roof over the upper rear/outer refrigerator. You can see it on the roof - it's the flat spot that the upper vent sits on. So the cavity left over when you remove the fridge won't be a completely perfect "square."
4) By looking up the installation manual for the RM3663 (that's the Dometic refrigerator that came in my rig), I was able to get an idea of the size of the "hole" ahead of time. They call for a space that's 23-11/16" wide, 53-3/4 tall [however see note above about "perfect square"), and 24" deep. So that gives you an idea of the space you have to work with. Since a compressor refrigerator doesn't have a complete "pachinko machine" of tubes, burner, and etc. behind it, you will generally find that a refrigerator with the same exterior dimensions will have a larger cubic footage interior. Or, conversely, you can have the same (or smaller) interior size and add more insulation.
In my case I wanted a "going out the door set down" counter above the refrigerator plus a wider hallway, and I'm not feeding a family of four, so I purposely went with a smaller refrigerator. I went with a Vitrifrigo 130. A friend who had the same "hole" left over (not a Chinook but same old propane refrigerator) went with a Vitrifrigo 150. This is a medium sized refrigerator with a separate freezer door (mine has the plastic flap door inside) and we were able to put vast amounts of insulation around it plus make a "pan locker" in some extra height space. Don't quote me on it but I think the Vitrifrigo DP2600 would fit the hole with just a little bit of extra space for insulation and is actually larger inside than our originals (I think it's like 8 cu. feet). But of course check on the space if you are going to buy one (edit: Oh, I think member pdemarest might have installed a DP2600 so could say how it fit). I found that Sure Marine has a GREAT multi brand size comparison which you can order by Brand, height, capacity, width, etc. Here is a link to that. I bought my refrigerator (among other things) from them and they are good folks.
http://www.suremarineservice.com/Refrig ... rison.aspx
I like to look for a refrigerator with a Danfoss compressor, but there are other good options as well.
5) For replacing the MDF, I used a multiply type plywood, but there are other good options as well. A marine ply would be even more water resistant, but I wanted multiply for other reasons, and it's already much less "sponge like" than MDF (which is both heavy and prone to puffing/disintegrating when wet… whoopee). It kind of depends on if you are trying to match your interior/re-use the original doors, go for a different look, or whatever. I was "off the hook," as I didn't like the oak raised-panel doors (just not my style).
If I got off track, or missed something in your questions, feel free to re-ask.
BG