In reply to crayefish:
A quick glance at the Norwiegen customs website shows they operate an identical system for exporters as the EU.
As a company you apply for a Nodi number ( in the EU EORI number). Then you buy or normally lease the TVINN software (in the EU ATLAS) and get an approved secure internet provider. After a test period you will be then qualified to operate the software connection and can apply for a shipment number ( in the EU a Movement Registation Number) and can pack and ship the goods through the specified customs centre. To get an idea how bad all this is just to apply for a MRN the advisory document is 190 pages long, I read it last week. For smaller values (under €1000) Germany operates a simplified system but for Norway I don't know.
For all exports into the EU you also need ALL the relevant paperwork if the product requires a CE mark and show who is holding the relevant technical files inside the EU.
This is why leaving the EU is dreaded by UK businesses, free-trade agreement or not you still have to do all this sh*t.
And I haven't mentioned the hassle of reclaiming the Norwiegen VAT and import duty that was paid when it was imported.