The about $199 Gator Cases Creative Pro 27" iMac Carry Tote is doing a great job protecting the iMac 5K, and it can be set up in under a minute and used even without removing it from the bag, although for extended use it is best to remove it for ergonomic and heat reasons.
Well worth the price, for anyone traveling with an iMac 5K as I am.
As shown below, the Xantrex 3012 3000 watt power inverter was too big and has been swapped out for the Xantrex Freedom XC. The van is not finished (walls in particular), and I am still using the temporary table as shown with a 2015 iMac 5K and the NEC PA302W wide gamut professional display powered by a 5 kilowatt Lithionics battery, good for about 20 hours of computing as shown. The iMac and display are stowed when driving. The Yeti Tundra 210 cooler seen at left is part of the bed platform.