Hopefully this helps someone else who is a n00bie like me.
We were trying to fill the fresh water tank on our 2016 3011DS for the first time last weekend and could not get water into the tank. We have about a foot of hose with the end cut off and stuck it into the fill hole but water would just pour out of the hole. Had to take the mattress off, remove the plywood, and then remove the hose clamp holding the hose about 6 inches higher than both the fill hole and the tank. Once that was done, it fills perfectly.
I guess this is the "fun" part of having a new RV.
and this is my first RV of any type so the learning curve has been fun the past few weeks.