Looking at 3 inch temperpedic topper for rv king . The topper will measure 76” and mattress is 72”. Also , the temperpedic is very heavy, will it be too heavy for bed when the slide in moves and will the bed lifts still hold up bed when utilizing storage beneath? I had too much weight stored under bed last year and the bed frame came apart . Also , will I need to trim the topper or will it still fit when sheet is tucked in?