3 minor "innovations" in rocket mass heaters

I have gotten a lot of good ideas from this forum as well as Erica and Ernie Wisner's book. I thought it was high time for me to contribute now that I have some idea what I am doing. The only rmh I have ever seen in real life is the one I built so I don't really have anything to compare mine to. I also don't have any scientific equipment to measure heat transfer so I don't know if my insulation "innovation stacks up with other methods. Below are my 3 ideas.
1. I used 2 rows of beer bottles instead of a slab for a base. The outer bottles were laid in regular cement mortar and the inner ones were bedded in sand. (I should have added a vapor barrier)  I also added bottles wherever I could to the cob surrounding the firebox.
2. I did a cast riser but couldn't find a grease drum for the outer casing so I joined a 6 and 8 inch stovepipe to make a 14 inch diameter Tobe.
3. I made the bench run along a earthbag/cob wall to make a lot of thermal mass.

I use beer bottles to reduce the amount of material needed.
But what advantage would they serve in your case?

The beer bottles definitely saved me mixing more cob than I had to (thus saving my poor back lol) but I mostly was using them for insulation. Apparently back in the day beer bottles were used in slab floors as the trapped air in the bottles acts as insulation. A lot of people who build pizza ovens also use bottles under the floor of the oven to keep heat from radiating downward. The cob I used also had perlite mixed in as per ernie and Erica Weisners book.

Hi Wills;
1) I like your bottle idea to insulate from your floor, it should work great.
I might choose to use a heavier-weight bottle, but if you have beer bottles in aplenty, then that is what you use!
2) Creating your own outer barrel with sheet metal (stove pipe) has been done before, what did you use as an inner form?
I have had great success using round cardboard (sonitube) concrete forms as my inner form.
These burn off with your first fire leaving a smooth perlite / clay liner.
3) Alway utilize a nearby mass to help store your heat.
With the exception of a wall that could transfer that heat to the outdoors.

Looking at your photo, I'm hoping that the horizontal pipe we see, is now covered by cob.
If not that could be a problem. An exposed pipe sheds its heat so fast that your gasses will cool too quickly.
This causes condensation and possibly stalling the draft.

How long have you had your RMH?
Do you have more photos?  

Oh that's an old picture. My bench is fully cobbed but not lime plastered yet and I have used my rmh 2 winters now and I love it.
The wall is an interior wall so I'm good to go there.
I did an informal weight test on the beer bottles (calculated the psi that the mass would exert on the bottles) and figured they were good to go. I am 180 lbs and I can jump up and down on a beer bottle.
I used 8 inch stovepipe for the inside of the riser. It burned out but it held long enough.
I will take a picture of how it looks now when I get home.

Here is a more finished picture of my rmh. I burn slash pine in it and it uses maybe a half cord per winter.

If anybody is interested in how to build a slab with beer bottles in it I recently got a few pictures from a project I did similarly. I used 1 part cement to three parts sand to make the mortar.