MoonMan's UPAC is a great design. Problem with a spray pump like his it's possible to flood the atty. His feeds into the cart (with filler) and thus it's harder to flood but not impossible. Squeeze bottles work so well because of the vacuum effect upon bottle release (i.e. excess liquid is sucked back into the bottle). There's also been some reports of the draw suction pulling juice from the bottle into the atty, sort of an auto-feed effect. That'd be the holy grail but at this point nobody's perfected it. There's so many factors that it may never be perfected without a much more complicated design (i.e. adjustable inlet tube for different liquid viscosities/draw strength, etc...)
My next mod I'm going to do a JB type, and I have a bunch of reasons I want to use a spray bottle but I want to bottom feed. The spray heads I have deliver 2 drops per pump, but I'm still concerned about the lack of suction.
Someone much wiser than me will eventually figure it out!
For plastic molding, there's lots of options. The mAhmba 2.0 actually uses pvc pipe elbows to form the top! The bottom is machined aluminum, and the sides are plastic. Depending upon your shape's complication you might also consider having it 3D printed like Darchand's famous e-pipe!
