Getting the fridge to work as a dual zone would all depend on where the thermocouple (sensor) for the thermostat sits. If you can get the foam to sit above the thermocouple, then you can use the foam to trap a layer of air around it and it will maintain the temp based on what it reads in that reduced space.
The Engel dual zones only have the cooling bit up one end of the box and a vertical moveable baffle. The others won't work quite as well as there is still room for the air to move around the cooling fins, but will probably work well enough for what you want if you keep the frozen stuff filling the bottom 2/3rds.
I'd suggest you cut up a Kmart closed cell fitness mat as it will insulate well, be able to be rinsed off if there are spillages and is all of $7.50.
I don't think you will have much luck vac bagging bread. The whole point of it is that it is full of air holes. Sucking all of them out gives nothing but disappointment.
As you found, trying to vac bag it with no protection will give you flat bread. Sticking it in a protective structure will probably allow you to draw a vacuum, but will defeat the purpose as it will probably freeze dry the bread and not actually reduce its volume, so when thawed you get prematurely stale bread that still took up too much room in the fridge.
Pulling a really good vacuum will suck the air out of the bubbles, then when you release the vacuum, atmospheric pressure will squish the bread anyway.
My suggestions would be:
a. Stick the load in the freezes overnight before transferring it into the car fridge. If you can get dual zone sort of set up to work, all the better. Try and protect it with some sort of structure (folded cardboard??) as heavy stuff will still squish it.
b. Bake fresh bread. If you couldn't be arsed mixing flour and waiting for it to rise while camping, then get some bread mix and make it up at home. But instead of letting it rise the first time, glad-wrap it and bung it in the freezer. Pull it out at lunchtime and by dinner it should of thawed and hopefully risen and be ready to bake.
c. grab some balls of pizza dough from Woolies and pretend its bread because it basically is really. https://www.woolworths.com.au/shop/productdetails/965942/picasso-pizza-dough-ball
d. learn to love damper.