We bought a used 2007 SS 2860 in 2008 from a local RV rental company. I was very pleased with the fit and finish.
No big problems with it. One slide was not working properly but I lived with it. I have a hunch that it was damaged and then mis-aligned. My only big complaint was that the generator exhaust was under the fore-mentioned slide and had problems with exhaust smell unless there was enough breeze. Even if the slide didn't have problems I felt it wasn't the best designed.
The furniture wasn't the greatest. The MasterCraft couch had a broken spring and the front seats were uncomfortable. Replaced the couch, took out the dinette and replaced with a small chair so the DW could rock, and had the front seats redone.
I think the coldest we were ever in it was in the low 20s. No their are not a four seasons rig, the furnace was a 30,000 btu (?) and it did fine.
The last time we were at a RV show in 2013 we looked at a new version of the 2860 and we both felt that it was a good bang for the buck. Seemed as though it was better than some of the mid entry A's or the dealer fixed it up before they displayed it.
The Forester line is the same as the Sunseeker but some more bells and whistles. You might do some comparing. Forest River has a forum that you may find helpful too. http://www.forestriverforums.com/forums/