The Railpass allows the holder to travel on 2nd and 3rd class on all SRT trains (local, rapid, express and special express) with or without air-conditioned, day time seat or overnight berth. This is the new 2nd class air-con sleeper, i took the upper bunk from Hatyai to Bangkok, 945km in 17 hours... I'm loving it ! Did you see my towel hanging there? i even took a shower in the toilet too. Once in a life time experience !
This is the non air-conditioned (but with fans) 2nd class sleeper, what a huge difference from the new A/C sleeper above, but the difference in ticket price is just minimal. you wont feel hot even if this coach is not air-conditioned, because there will be breeze from outside when the train is in motion, but it is definitely noisier