Hi Tango,
My preference is for slotted foam - I just think rippled foam for example tears up over time.
What size of box were you thinking of? I've a short and long slotted one which I can photo and post tonight for possibly a better idea. One point of note - I don't use them as they are bulkier than a 'standard' box (C&F, airflo, for example) less bulk when on the river is better for me.
Not an issue if you carry your kit in a bag, etc.
Iain