As far as I can tell, the Terrain rear slide is built the same as the previous model Outback 250RS. I have a 2011 250RS...this topic has been thoroughly discussed and researched over on Outbackers.com and keystoneRV.org. The final answer was do NOT put extra weight on it while it is stowed in. For those who absolutely want/need to use it while in, many of us have crafted under-slide supports for use when it is in. I even use my support while towing the vehicle as it did start to pull the ceiling guiderails out.
The weight limit for when it is extended would be...2 adults.