I got it working, had to use namespaceMappings as following:
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
@"http://howdoi.org/",
@"howdoi",
nil];
NSArray *items = [doc nodesForXPath:@"//howdoi:VehicleUnit" namespaceMappings:dict error:nil];
This sets the array to 11 items and let me do what i want :)