FWIW...I'd be doubtful that your Sunseeker could be beefed up enough to handle 600 lb. tongue weight PLUS the weight of the rack... and believe you should check with Ford. I think you'll need an air bag spring lift system at the very least & I've never seen a hinged version that could hold that level of weight dynamically. You also need to calculate the lever arm effect of your static weight since the bike sits well outboard of the frame. Don't just think 600 lbss is all you need to think about...my 600 lbs added roughly 1100 lbs to my rear axel load dynamically. Make sure your coach and rear axle GVWR and GaWR have plenty of spare room since you are not towing extra weight but carrying it.
If you do have the ability to carry your MP3, Versa Haul mkes a high quality unit. Piaggio MP3 Carrier from VersaHaul VH-MP3 | DiscountRamps.com
The other alternative which might be right for your situation is the swivel wheel whch will both work without modifiying and flips up when not in use.