All, Well, I've done it now. I brought home a new class A. Mine is on the FORD F53 chassis. The oil fill cap & owners manual state it is to use 5W20 motor oil ? WOW! That sure is thin....
Do you want to listen to the manufacturer who designed and built it or random guys on the internet for the proper oil?
As far as leaving the slides out, in principal it shouldn't matter but unless you are inside using it on a regular basis, why leave them open. As someone else mentioned, the slide toppers get caught by the wind and experience UV damage being unrolled.