I drove a portion of the White Rim trail in Canyonlands back in July 1976 in a 2wd Datsun Pickup. We took a steep, nerve racking road from the rim up to the top of the Island in the Sky and, half way up, ran into some guy coming down in a Chrysler sedan. That was impressive. I wondered how the rest of his trip worked out. It was over July 4th (the bicentennial of the USA) and temps hit 100+. Great Trip. I think that it may have been in National Monument status at the time, prior to it becoming a National Park. Things were a bit looser then, no permits needed. Of course, that was then and this is now. I suspect things have changed a bit since. So, I actually don't have any good tips that would be helpful for your trim in April, other than enjoy yourself, as it is a truly beautiful place. Take some photos for posting and have a safe trip.