We put toppers on our '19 295RL shortly after purchasing it too. We mounted them to the factory installed rails which also made them somewhat "shallow" pitched.
Our fix for the water buildup issue was to purchase suction cups and a stretch cord - 2 cups per topper. By centering the stretch cord and cups over the length of the extended topper (which only takes a few minutes to put on/off), and letting the weight of the cord alone, no additional taughtness applied, and then cord secured to the cups which are suctioned to the slide, we reduced 95% of any accumulated water and topper wind sailing. For over 5 years its worked incredibly well and we still use today when camping.
As for sweeping between the topper and slide roof, never had to do it since installed, and slide roofs still look great. Upper seal maint is an issue, however, since no direct sun or heavy dirt collection, they have held up well with limited maint given.
IMO, toppers are the best mod done to our RV. No more climbing up to sweep off the slide roof before retracting, very little maint along with slide roof protection, reduced UV heat, and less rain noise.