Any advantage to sand between barrels?

I'm wanting to build a stove for my occasionally used 24x48x12 shop. I wanted to do a RMH, but after reading about them again, I found they are not good for occasional use areas. I was thinking of a double barrel stove. After reading more about them and how to improve them I think that is the way I'll go.
I have a very large fuel oil tank, I'd guess 350 or 400 gallon. My question is, would putting a 55 gallon barrel in this large tank and filling the space with sand gain me anything?
My rough plan is 55 gallon in large tank, then add another barrel on top of that with tubes from front to back for warm air flow and a fan behind that.
I'm thinking this top barrel would give "now" heat and the sand would absorb heat and give it off slowly.
I also thought about stacking concrete blocks around the whole thing for more thermal storage....

What am I missing?
Thanks!

Sand insulates due to all the air gaps between the grains.  So, you'd lose heat.

So, would rocks be better? Or concrete?

A traditional RMH with a thick mass would not work well for a shop, but you can build it with thinner mass walls that hold heat for just a few hours, and a barrel for instant radiation.

You could put a rocket combustion core inside your oil tank and have a huge radiator, with as much cob or brick around it as you find gives the thermal mass that works for you. This can be tweaked repeatedly with ease until you like the performance. You could even cut an access panel into the tank (a wise practice anyway for maintenance), and put bricks inside the tank wall so they don't take up extra space and are protected from traffic.
Brick bell shop heater

OK. Thanks.

Glenn Herbert wrote:A traditional RMH with a thick mass would not work well for a shop, but you can build it with thinner mass walls that hold heat for just a few hours, and a barrel for instant radiation.

You could put a rocket combustion core inside your oil tank and have a huge radiator, with as much cob or brick around it as you find gives the thermal mass that works for you. This can be tweaked repeatedly with ease until you like the performance. You could even cut an access panel into the tank (a wise practice anyway for maintenance), and put bricks inside the tank wall so they don't take up extra space and are protected from traffic.
Brick bell shop heater

Would I really need to use the oil tank for anything other than a container? Couldn't I just stack bricks or blocks around the core?

Glenn Herbert wrote:A traditional RMH with a thick mass would not work well for a shop, but you can build it with thinner mass walls that hold heat for just a few hours, and a barrel for instant radiation.

You could put a rocket combustion core inside your oil tank and have a huge radiator, with as much cob or brick around it as you find gives the thermal mass that works for you. This can be tweaked repeatedly with ease until you like the performance. You could even cut an access panel into the tank (a wise practice anyway for maintenance), and put bricks inside the tank wall so they don't take up extra space and are protected from traffic.
Brick bell shop heater

The core needs to be insulated so it stays freaky hot inside; after the gases exit the heat riser, they need to be contained and ultimately (after giving up most of their heat) routed to the chimney. The oil tank would work very well for this, being airtight. Thermal mass could be placed anywhere around or inside it, even as an isolated column of bricks in the middle. The more bare steel wall, the more instant heat you will get.

The brick bell shop heater in the link would become in your case the tank replacing both barrel and hollow brick box, with as much brick/block as desired stacked around or inside it.