actually waterproof rainsheet suggestions?

hey i was just wondering if anyone has a suggestion or review of a rainsheet/rainsheets that youve had because im looking for one for my TB who has been hard to get weight on before winter this year. its started raining a lot lately and i want to at least keep him dry when its 45 degrees at night =/ i want him to get a good winter coat, so i dont want to start actually blanketing him yet. thanks and lemme know your experiences!