Just a thought - not all trade with the EU is by truck via Dover
I wonder what airfreight are planning to do? Heathrow does handle quite a bit of freight (as do other UK airports), and has somewhat limited parking (compared to Kent). Of course not all of air freight into the UK comes from or goes to the EU, but they will have the same problems, plus, of course, some products go by air as they are perishable or urgent delivery.
I expect someone has already mentioned this, but it is almost as if HMG did not have a completed, thought through and worked out plan for this Brexit thingy after all.
I suspect that one of the problems is this current government's propensity to build everything from scratch anew, rather than looking around to see what is available that actually works, or could be made to work reasonably quickly, despite the fact of Not Invented Here.
(Not expecting any replies or thumbs as there are now over 200 comments on this thread, and I confess to not actually reading all of them before posting, sorry.)