Older RV's used to use a gravity fill type system that placed the fill point higher than the tank. As near as I can tell, this has changed (at least on the larger RV's) to a pressure fill system that is located in the wet bay (usually convenient).
In my case, I installed a hose reel in the wet bay that is permanently connected to the plumbing system (thru pressure regulator, then filters, then to a valve that is either the 'system' or 'tank fill'. I pull out this hose and connect to whatever is available - no need to attach any extra stuff (pressure regulator, filter). Very old photo but gives you the idea...