I,ve had 3 vans now been able at the local key cutting stalls to get keys cut can.t remember the price but certainly not excessive. I have one on the car keys and 2 on lanyards which we can both carry if going separate ways . Now all the hatches and lockers are a different matter.
I got duplicates made at one of those key cutting shoe/watch repairers kiosks in the local shopping centre. But that was 20 years ago & pretty basic locks. Cheap.
I used to wire spares for van & tug on the chassis somewhere but either they fell of or I could never find them again.
I gave up & now carry spare van keys in the Patrol & spare Patrol keys in the van. All have a long lanyard & the spares have a big lump of ply wood attached. I do similar with amenities and entry keys/cards .. ie lanyards & big name tags.
We have an Avan Erin Mk2. We've always been under the impression that you have to order additional keys from Avan.
The doors come from Germany or Holland? I've tried searching this forums archives because someone recently posted the same question that you have, they managed to get one cut cheaply without all the mucking around.
Unfortunately I can't find the thread that they started.