Anyway I can see those vikings being able to establish their own stem duchy Frisia. Hopefully they'll be able to protect Dorestad (commercial centre; IOTL vikings raids brought its' demise.
They did hold Dorestad for some time; the regular raids was due to the Jutish/Frisian royal line having rebelled against their overlords in Scandinavia thus getting as deserved.
ITTL they would rather be party to the raids and Frisia a secure base for most of the journey to the rich playgrounds of England and West Frankish empire.