So how could you make it more successful?
It's likely that Danes
were successful in Frisia, at the point being largely integrated into local society.
But I think you wondered how make it more of an independent principality?
Their main problem was these charges were given in context where both the imperial power was still existing but weakening, and where nobiliar power wasn't that settled it became.
The lack of matrimonial alliances with a nobility that became the obvious natural political partner was really problematic for Gotfried, for exemple : he pissed everyone in sight, didn't stopped raids, and made alliances with the "wrong sort".
Basically you need acceptance from local nobility, a weak royal/imperial power in order to be acknowledged and politically useful (Ragenold was called to help by Charles, for exemple), military victories and strong political patronage (as Robertians did).
A quite narrow window of opportunity, but with the early Xth, doable. I could see a Norman Frisia would Gotfried having been more competent, or even a son of Roric succeeding him, maybe not directly as a Frisian ruler, but at least as established in Frisian/Lotharingian nobility. I'd think that in this latter case, the identification with local populations would have been even stronger than in historical Normandy
It would have been interesting with a scenario where it was a Normandy based on the Lower Rhine, and not in France, that conquered England.
That said, a Normandy based on the Lower Rhine would have a more limited marge of manoeuvre than the historical one : while the links between Late Anglo Saxon spain and Germany are known, they beneficied less to local nobility than the royal house (see Harold's campaign in Flanders).
The whole connection with Normandy, before the conquest itself as you had Norman councilors in AS court (maybe coming down from the Anglo-Scandinavian settlement of Normandy) may simply not exist with this alternate variant.