The factory caps don't seem to be vented.
I have to loosen the cap if I am using the nozzle, but the genny uses little enough that the venting does not seem to be an issue.
As to putting fuel in, if you look at the level of the tank, and the level of the inlet it is easy to see why there can be splash back. That is also the reason it is very difficult to put fuel in using 5 gallon jugs.
Other brand toy haulers had the fill pipe much higher, and the pipe came up through the garage floor and was trimmed to be hidden, but it took up garage space.
The early Cyclones advertised no impingement into the garage area with the fuel fill.
So it is a trade off. Open floor in the garage and a low entry pipe or a bump out in you garage to trip over or get in the way.
The first toy hauler I looked at to buy had the bump outs, seeing those I prefer the flat floor.