Don't see any requirement other than 'gun rack'. Also, wanted to make sure you notice that twoguns? bolding of that statute caused me to change my answer to #5.1 and #5.2 as it states concealed behind the seat or in the interior as long as not clip, magazine or chamber loaded.
This is what I was looking at UMB...behind/under the back seat in a 4 door pick-up.
Is that a ..trunk?