full hydration, natural levain, wholegrain loaves in a gas static with no DO?

For the past few weeks I have been baking out of a school kitchen trying to prepare to sell to my local community. However, I can't seem to get a gas static oven to work and wondering if anyone can give advice on tuning so that:

- I don't need to buy dutch ovens or a lot of other equipment

- i can continue to use wholemeal flour from the wholegrain of wheat

This might be an impossible ask. I have a home oven (small), electric and fan forced. I can create a good loaf in here:

It might not be a great loaf yet but it is good. Some notes:

- at home my hydration percent is between 90 - 100% and I'm using Australian wholemeal (wholegrain) flour at 13.5% protein.  

- extended autolyse without salt or levain

- I do fewer sets of stretch and folds predating the bulk rise

- as i will be baking in a school, I need to use their coldroom at strange hours so that's why I break the process in the middle (that's been successful at home).  

- temperature is low to mid 20s

- bulk rise does not rise up in the tub very much (I assume it's this flour)

- when it goes in the oven, it is not in a dutch oven although i do introduce steam via muffin trays of water in the base of the oven.

It comes out quite dark (but tasty!):

and it's something i can replicate over and over again at home:

but using the following ovens (at the school) I am getting a different result:

This is a gas fired oven and the fan is strong. It is listed as "blue seal" static oven, sometimes known by Moffat branding. I suspect all loaves are crusting too early and the expanding gases can't escape. The loaves from this oven are significantly heavier (in weight) from those baked at home. They are shinnier. They are pale (more pale than those at home). They are flatter (as if over-proofed) and inedible. They look like this:

So yesterday I tried a bunch of methods to introduce steam. Methods included:

- putting the temp to 300 Celcius and preheating the interior of the oven, including the cast iron baseplate. Turn off the oven when the bread is put in (turning the oven off turns of the fan automatically) and leaving it of for 10 minutes before putting it back on. 

- as above but placing the loaf on a tray directly onto the cast iron base-plate

- as above, spraying the walls with water pistol when putting the bread in (and heating muffin trays of water in the oven before switching it off)

None seemed to work effectively:

Any ideas on next experiments welcomed. Again, the goal is to get an acceptable loaf using these ovens but without using dutch ovens inside them.