Be sure to save your RVT model immediately prior to importing any of the PlaceMaker data. That way, if there is a crash or you lose your imported data for some reason, you should be able to reselect the same toposurface and reimport the exact same data from your cache without having to spend more credits.
For this to work, you need to use the same import source / type and settings and reselect the exact same surface prior to re-importing. Then, you can redownload most data without using credits (except for Terrain which cannot be cached). Watch the video below to see the process in action.