When my Body Corporate bought a bunch of IKEA outdoor furniture for our communal terrace I grabbed a large quantity of large cardboard boxes and packing with a view to using it to provide a system for making more realistic land forms in greater variety.
The hinged sets fold up flat for compact storage - much easier to store than the usual 3-D hills. The storage boxes stack away neatly under the wargames table & continue in use for storage whether they are on or under the table. The pic above is a stack of about 60 square feet of hill formers flat packed for storage.
The system is still a work in progress but I think it's looking good & I still have lots of cardboard left.