I'm using exactly the same painting material at home and for plein air. I found a perfect organization with a box that I completely transformed at my convenience. I'm using it on a table for my small paintings at home and recently adapted 3 feet for plein air which iwork perfectly. Everything fit just right into a bag and remains quite light and handy to carry.
My box in tuscany
A picture of the view I had and my painting below.
On the far right I could see Siena in the distance
It was the first time I painted such a long size (21.5inch) with my box but it worked well