So many options out there, none really worked for me.
I want relative low cost, study, stackable, portable & flexible use.
I have 6 mm Hail Caesar with some bases up to 80 x 50 mm deep.
6 mm Black Powder 60 x 30 mm deep
10 mm Warmaster 3 bases of 40 x 20mm
Height varies depending standards, cavalry (Kontos), fantastic beasts or flyers.
As a club we started using 9 &4 litre really useful boxes, sturdy
easy to stack and carry.
4 litre 2 tray insert
9 litre 4 tray insets
Extra large 9 litre 5 trays
Not that we used this often.
We bought these with hobby trays that have 15 sections we can get 30 of our 60 x 30 mm bases.
The models are quite snug and tend not to move about. Each 35 mm tray allows for 32 mm height.
You can cut up magnetic sheets 60 x 60 mm to fit the squares, not glued and metallic paper to the model, the paired bases can't flip.
However BKC2 10 mm needing 40 x 20 mm, not as snug and vehicles that used one spot only and our 20 mm RF models, vehicles don't fit and individual based models were falling over they're top heavy compared to 6 & 10 mm multi based models. We looked for alternates home made tray inserts.
A solution for me was the 11 litre and 21 litre boxes into which I placed foam trays. 2 in 11 litre, 4-5 in 21 litre, 6 in Extended 21 litre box.
This 21 litre box contains 4 trays as the dragon model is so high there is no space for a full 5th tray though I could use half a tray. Without that model there is space for 5 trays = 200 of 40 x 20 mm bases, sturdy stackable.
But as you know many GW models extend beyond the foam and banners and weapons can be bent or broken off.
Not just the Wyvern!
Finally a friend mentioned the problem to Walter Anstiss of commission-figurines and at last we had a solution.
These trays are self assembly when ordering choose to have one or two central bars as shown above, the difference suits different basing systems.
For my 6 mm Hail Caesar I have one divider and get 2 x 20 mm trays and 2 x 30 m and 1 x 40. Total possible is 140.
This has allowed me to get a Dacian, Sarmatian with Kontos and Roman armies plus extras in.
As for my Warmaster the Undead horde that filled a 21 ltr box (5 foam trays) now all fits in one 9 ltr box, easier to store, but just as heavy!
These models are 10 and because of the banners I chose to use 3 x40 mm and 1 x 20 mm at the top for archer and bone throwers. I also cut the bottom out of half the top 20 mm tray so I had a full 60mm clearance for the dragon and other models that needed 40+ mm.
I use blank bases to fill the gaps to stop the units sliding.
Although wood bases on wood trays has a lot of friction for the larger or loose models I use Stopp from IKEA (for lining kitchen draws its stops the models sliding about.
It's relatively thin so wont waste height, low cost too.
Hope the above helps.