Trading in sterling for a transitional period would mean goods from Scotland will avoid currency exchange issues.  If the UK doesn’t sort its borders with the EU, the resulting fall in the value of sterling will mean that trade with the rest of the UK increases, not decreases. Scotland will be the only nation from which rUK can afford to import. Where else would the rUK get the oil, electricity and food it needs from? It will be cheaper and just as easy to import from Scotland.

Failure to sort out the current border chaos would mean the UK economy would be in free-fall and, given that Scotland exports more than twice the amount of goods per head than rUK, our economy would be hardest hit.

An independent Scotland in the EU would have the same border checks as the UK has.  With the right agreement border checks can be electronic, pretty seamless and not physical whether in or out of the EU.