I agree about the monotube. At the least, it would be unpleasantly bouncy with 375 pounds on it. The Sun series, especially the steel models, would be better. By happy circumstance, the steel ones are less expensive! The seat might have to be strengthened, the base is (I think) only plywood. A couple layers of carbon would do the trick! And the wheels might not last long. If the wheels start failing, they could be replaced with higher-spoke-count ones.