Walter de Cornwall - Sources Request

I'm trying to validate information provided for the marriage and children of Walter of Cornwall. Rootsweb is an unreliable source because we don't know where the information comes from most of the time and therefore we cannot validate such information. I would like to know if anyone can provide reliable sources that validate the information provided above. I like The Complete Peerage because it is well researched, although it also has to, at times, be scrutinized. I also like Foundation for Medieval Genealogy and find it very reliable. In both cases, there is a ton of research involved. In this case, the maternal parentage of Walter is uncertain and in one case is attributed to Beatrice and in another to Joan. I have been unable to find yet any sources that validate that he had any children. That is the purpose of this discussion - to verify a) that he was indeed married and b) that he had issue.