late 70s-early 80s doublewide roof issues

[Fran365]

I bought a double wide (24'x64) in 1990.At the time of sale the owner had done a 20G fix on the roof, trusses beefed up, new sheathing and shingles. I am not privy to the details of the trusses repairs. A few years ago all the vents (plastic) started to leak and where replaced. At that time I looked into all the vent holes and saw no issues, dry wood and sheathing like new. We had over time removed many of the interior walls for an open floor design, and, a little concerned about the 24' span with no center support I installed a 4x8 ceiling beam down the center. The last 5 years there has been a gradual sag in the roof ridge area, perhaps 3-4", adjacent to this open floor area. So: my shingles and sheathing are good but this ominous sag- I am considering removing a 8 foot section of interior ceiling (center, that is 4 feet on each side of the center beam) to inspect and repair the sag. I've been surprised to see very little about this problem on line, there must be 1000's of folks with the same issues. I am hoping there is other ideas than rip of and replace. Anyone walked this roadf? Note roof pitch:3.5/12 and outer walls are not splayed out much (3/8ths-3/4") Fran

[Fran365]

Perhaps some clarification: What I am wondering is if I expose 8' off the center ceiling, remove the vapor barrier and ground up newspaper and set up lights, what will I see? With a stout beam running down the center could I use it to jack or brace the ridge area? When I get into this I'd like to post pics, can that be done here? Fran