Using variable sizes of panels when out painting can cause a few headaches in terms of storage/transportation. There are a few commercial options (mostly seem to be available n the US) but nothing seemed to be quite what I was after. In the end I decided to make a custom carrier that will hold my favourite sizes in one box and after plenty of head scratching and multiple visits to the DIY store this is the end result.

It’s 16in tall and has widths for 12in, 11in and 8in. That seemed quite a nice combination as I can store 12×16, 12×10, 11×14, 8×16, 8×12, 8×10 & 8×6 so that would hopefully cover enough formats to work with. 
It’s a bit heavier than I’d imagined but I think anything that size will have a bit of weight whatever the material (if it’s going to have some strength too). I used corrugated plastic sheets and the plastic panel holding grooves seemed worth trying as they had the right shape for the sort of panel depths I use (3mm mdf). I’ll need to make sure the panels are cut to the right widths as the ridges are only 4mm deep but that should be enough to allow for minor variations on board size. 
I opted for a hand carrier strap (as opposed to a shoulder one) and attached it with lots of glue/strapping to secure it. It’s got a velcro fastener so it can be undone or adjusted if necessary. The variable widths were built up with strips of foamboard glued together into solid blocks and on the outside I used plastic edging strips wherever two edges meet to provide more strength.


Lots of gaffer tape to seal everything up!
I think it’ll probably be too bulky for foreign trips (I usually use matchsticks on the backs of stacked boards for those) but it should be fine for domestic purposes and will hopefully make the carrying of wet panels a bit less problematic when using different sizes on a day out somewhere.