I was hoping to get a Strebor case, but they've stopped making camera cases, I gather. So meanwhile, on the odd occasion that I take the big camera out in the city, I put it on a luggage cart with my holders in a tote bag and lenses in another small shoulder bag and tripod on a strap over the other shoulder. My camera is about 18" square, and maybe 5" thick like yours.

At the moment I'm looking at one of the larger Calumet Waterproof cases (like Pelican). I think the second biggest one will fit, but these are quite heavy--about 30 lbs. for the case alone!

I think the Tenba Air Case for a Mac G5 tower would be perfect, but they are over $600, which is more than I want to spend on a case.