Hello James welcome to the forum.
Just a few helpful tricks for ceiling mounted DVD, there are many to choose from including sound options, If you looking to look at this for your viewing purposes as well TRY a SONY unit 9 inch screen High Definition, as it will swivel left to right and down to suite your eye level.
Fitting these to a ceiling is not an easy task, as to you have to be exact as to where it's placed, removing the lining is also a hard call, relocating wireing and trace back down a wall has to be planed in advance,
If using optional amps and surround speakers , you need an auto electrician to help you do it unless your competent to undertake a DYI installation
I noted you stated slopping ceiling as to a passenger unit vehicle so I assume you meant a Hi-Top model not standard roof either way you will have to set it back to the level portion of the roof paneling, or make up a mold for it to fit the unit! if you want it to the flush mounted front section,
Think about how it's done as to a safety issue in the event of an accident they can be dangerous if not correctly mounted.
Other option much easier dash mounted or rear seat mounting for passengers, buy a top end unit dash mounted which has the video in out for two additional screens along with multiple channel surround features.
Richard,
PS THESE UNITS COME WITH A METAL TEMPLATE TO LOCK THE UNIT INTO PLACE, BEHIND THE HEAD LINING, FOR CEILING MOUNTED UNITS ONLY
Sony 5.1 channels Video CD VCD DVD.JPG