Oh and the technology suggestion? If it really works then why hasnt it already been implemented at calais jungle to stop illegal immigration?
Presumably because checking for people hiding in the back of trucks on a border between EU member states is an entirely different concept to checking that importers of goods between the EU and a third country have paid the correct VAT and duties on the goods. That's what a hard border is all about - the 'people' part will be exactly the same unless and until we impose restrictions on EU citizens.
There's no connection between checking for people-smuggling and (at a basic level) checking that VAT returns are correct. And the proposed/imaginary 'technological solution' is mainly concerned with checking that VAT returns (and declarations of duty) are correct.
Checking for people- and contraband (drugs etc)-smuggling will continue to go on at the same level whether we're in the EU or a third country - except that staff currently doing that will probably be fucking about collecting £5 duty on an over-the-limit bottle of perfume, or checking that all 38 pages of a loading manifest have been signed.
A tiny proportion of non-EU imports are physically checked by Customs, the proportion will drop even lower when their resources are spread thinner (and obviously current 'EU-imports' will/may be treated exactly the same as we currently treat non-EU imports). Most (non-EU) imports go through without any problem because the customs declarations are assumed to be genuine - like most Self-Assessment tax returns and VAT returns go through without question because they're assumed to be genuine.
I've not had a question, visit or query from HMRC in the 20+ years I've been submitting returns for my current business and for myself for Income Tax, Corporation Tax, VAT, PAYE and a couple of minor things I won't go into. They check a tiny proportion of things and try really hard to target the potentially dodgy fuckers. It's exactly the same principle - they only physically check a tiny proportion of lorry loads.