After a lot of research we ordered a mattress from mattressinsider.com
The our 3170 Sunseeker platform does not support the sides of the mattress. There was 4" per side that was unsupported which eventually broke down on my side. We ordered a custom width to reduce the unsupported overhang. We are very pleased with our choose. And as a plus about 20lbs lighter than the upgraded OEM Serta.
2014 Sunseeker 3170 DSF
Dorothy, Garrette and Miss Bella.
Retired and having fun.