I d t think that it is leaking. I think it did just run down from the top...but I never had a slide do that before that's why I thought it was odd...
As for the mattress...I bought mine of the lot and it had the standard mattress. I'm not sure about the serta. I did sit on one at the show and it seemed better then the standard for sure...I love his memory foam mattress we got though hands down. Good luck with your when you get it..I recommend adding a surge protector...they can save a lot of headaches. Was the first thing I added...years ago we lost an air conditioner in the middle of the summer at myrtle beach...
2015 Dodge 2500 Big Horn 4x4 6.4 HEMI
2015 Grand Designs Reflections 323 BHS
Reese 16K Quick Slide with Factory Rail Kit Option