We use a belt over roller unit for moving rugs between floors. Daily use for 15 years with no maintenance issues. It's bigger than what you want and isn't meant to be used in a wet area, so not the answer for you.
If you don't want to search, give a local material handling company the parameters and let them do the work.
PS: I think you have the right answer to loading, one that the purveyors of centrifuge ringers might want to look into offering.