But there will still be checks on vehicles travelling from NI to rUK, because some will contain EU-sourced goods - full or part load - and for Unionists it is that sign of a 'border' that is surely the main issue, as trucks containing NI-only originated goods are held up by checks on other vehicles - or have to demonstrate in some way that they only contain NI-sourced goods.
Apart from that - I do like that Johnson was selling the benefits to NI of full single market access and freedom of movement. Pity the rUK won't have that and so by definition the rUK will be less advantaged...
For a mixed load, yes there will be checks. I have no problem with that. Not sure I agree with you about a line of trucks because the one at the front will be undergoing checks. Do you not think that trucks with EU goods will be directed to a different line, e.g. airport queues that has two lines at passport control? Imagine a queue of trucks with the last few still on the boat, holding up loading for the turnaround - its not going to happen.