I think the premise of closing your borders so as to have a normal life inside them is a good one
I don't see how it's a particularly feasible one. The UK is massively reliant on imports and a major international transit hub, our society and economy is not set up for long-term border closures. It's also inhumane - there are many people who, thanks to years of freedom of movement, have structured their lives around international travel and loved ones in other countries. It's completely unfair to pull the rug out from under them and the lives they built in good faith as a long-term strategy.
It also sounds bloody miserable. Who wants to be stuck on one little island for years on end?
I suppose it's easy for the SNP to posture about it - let England take the hit for all the goods coming in at Kent etc but play at being strict. Not sure what the legalities are of attempting to close a land border with the rest of the UK are but I suppose we'll find out soon enough.