Try these:
http://www.californiadelta.org/boatrents.htm
http://www.sevencrown.com/lakes/cali...elta/index.htm
http://www.houseboats.com/hermanandhelens/brochure.htm
http://www.houseboatrentalcenter.com/california.htm
Haven't been there in a long time but when we went they let us tow our boats behind the houseboat.
Good luck