If it works it works. Wouldn’t bother with the sand personally. Suspect it will just make the stone heat up more slowly. You’re not going to retain heat for very long so just use it for pizzas only and accept its limitations. Weber and the like all do pizza cooking accessories for theirs and as far as I can see it’s just a stone and something to prop the lid open. Never going to compete with a ‘proper’ oven but if it’s doing the job then all good.
It worked ok once I got it really hot but struggled a little with the stone not being hot enough to cook the base. This led me to think that if I either filled the base with sand or recreated a pizza oven floor it might improve the situation.
I have a Weber but I'm not a fan of the pizza attachment as I believe it isn't ideal, to much heat gets lost in the dome and there are many mixed reviews on its actual suitability.
I found similar with my first pizza oven which was a steel box version from Tesco. Different to yours but the same concept and no insulation. Limiting factor was the stone and although it cooked good tasting pizzas it was very slow and took a long time to reheat. If you have enough depth get yourself some heater storage bricks or some proper firebricks and lay those in instead of or in addition to the stone.
should i lay the entire base with them so the fuel and food are at the same height and effectively on the same base?
Best to experiment but that sounds sensible bearing in mind in a normal pizza oven that would be the traditional layout. Not sure if the shape of yours will lend itself to it but on mine it’s amazing how much cooking the rolling flame over the top of the pizza actually does. So much so that if I let the flames die out at all it’s really noticeable how much longer they take. All comparative bearing in mind mine only takes about 90 seconds to cook one.
If you were to put the fire underneath then the configuration would be much the same as my original Tesco oven which had fuel at the bottom, below the stone and cooked pizza in the top. It worked but more like an oven than a pizza oven if that makes sense.
The first one I had a couple of bits of wood but it didn't seem to cook very well, took about 10 minutes a pizza. Once I loaded it up with more wood it really took hold and got it down to about 3 minutes.
I had a half chimney of charcoal under the stone because I wanted it hot but not burning the base and the wood to the side, same level just sat on the grill.
Obviously I have cut the side out so I'm probably losing a fair amount of heat out the gap.
The main thing I'm trying to avoid is burnt bases and under-cooked toppings.