1. A frame for supporting a waterbed mattress comprising:
a substantially rectangular perimeter frame portion comprising opposed parallel side frame members and opposed parallel end frame members forming an enclosure for containing a flexible waterfilled bladder comprising said mattress to prevent lateral bulging of said mattress, and means forming a support deck for supporting said mattress, said side and end members being formed by elongated shallow channel section members having a vertically extending web and opposed generally horizontally extending flanges, the lower one of said flanges being adapted for supporting said frame on a bed sub-frame and the upper one said flanges forming a perimeter edge of said frame adjacent the sleeping surfaces of said mattress, and resilient cushion pad means extending along the outer sides of the webs of at least said side members and one of said end members, said pad means being formed to include a substantially horizontally extending slot along said side members and said at least one end member for receiving the peripheral edge of an article of bedclothing to retain said article covering said mattress.