Good morning DR yes grass certainly can be wonderfull to fly off out here in our parts its either asphalt or in most cases just desert hardpan 'arizona grass'
DR concerning the fueling valves, I tend to classify them with power panels. Just a complete waste of money and most certainly at least one lost flying day eventually fiddling with the engine when they start to leak and causing mystery running problems. I do on occasion acquire some on buy outs and such but immediately send them to the bin. I would not even give them away to friends simply because that's no way to treat a friend.
The three line systems with a fuel dot is probably the most popular way to fuel but I prefer the much simpler two line system (cowling or not makes no difference) with a simple split in the carb line where its convienent and a short piece tube to connect. fueling from here is the simplest and most convienent of all and least trouble prone.
I have pictures of many many different types of airplanes with and without cowls to illustrate this simple technique. Try searching on fuel valve or fueling you will most likely run across some of them.
John