Personally I like working on the back drop in adobe photoshop so i have much better control of things. For under water scenes it rules . What kind of backdrops were you looking for ?? Theres plenty of dungeons and sci fi backdrops . I love transponds stuff . They have a new one called "Toil and Trouble" . Thing about there stuff is camera angle . You can make 1000's of different looking backdrops from each product . Change the lighting or change the camera angle , its all there. Daz's has a new one called " Multiplane Cyclorama " is pretty good and easy to use. It takes 2d photos and makes a back ground but it lacks some for shadowning and real 3d look. If you like Victorian stuff there are some real good rooms out there with lots of nice add - on textures and furniture .
For sci-fi stuff DNA is were you want to go.