That pan really is not necessary. Looks like you might have an enclosed underbelly, so it just helps keep the water,/mice out. But it is not necessary.
My valve is supported by a small piece of lightweight angle iron. Personally, I would buy a 1/4 turn, 1/2" valve from the local DIY store and make a bracket. There was a discussion on this early this spring.
2012 Jayco X23B
2020 Ram Laramie 3500 SRW Air ride 50Gal fuel tank.
2007 Dodge Dakota Quad Cab (retired from towing)
Equal-I-zer 4-Point Sway Control