Need help setting up a video airplay solution for the car

Ok, sorry if this has been outlined elsewhere...I couldn't find a definitive answer, and the solution that I arrived at almost works...but hope smarter folks can point me in an improved direction.

Long story short--I have most of my video and audio media in the cloud now...Slingbox, iTunes, Amazon, Pandora, Netflix, Spotify, YouTube. My family all have iPhone 5s now and newer lightning-connected iPads. No 30-pin connectors that would make it easier to just hardwire devices to an RCA-based analog input...certainly none with cellular connections. I don't want to pay for an additional MiFi or similar device, and I'm trying to avoid using and paying for the Hotspot feature on my iPhone. I don't need to share an internet connection.

We travel in the car on road trips a lot, and I want to enable the car to be able to Airplay to the car's video system for media through our mobile over-the-air internet connections. Kivic One is the one video solution I've found online that is a one-box system, but I figured out (and confirmed online) that an Airport Express--Apple TV--HDMItoRCA Converter solution, when configured properly, will work too...mostly. I own all those devices now, so I figured I will try to make this solution work first before considering a $250 investment in the Kivic One, which doesn't have a ton of reviews online yet given it still appears to be in Beta.

As discussed on numerous other forums, the wireless network when configured with DHCP essentially makes the iPhone turn off it's cellular data connection. Changing it to a static IP config, however, seems to be the way around this, and this does appear to work for me. I am able to use Slingbox successfully this way, and all the music solutions appear to be working (Pandora and Amazon anyway).

Here are my remaining questions:

• Netflix throws a connection error. If I take my iphone off of the static wireless network (with no internet, obviously), it works over the air as you would expect, and when I put in on a wireless network with internet (in the house), it works. Is this a software limitation with the Netflix app? Can anyone else duplicate this?
• YouTube plays the video fine, but has no sound. Same thing--works fine cellular only or wifi-internet only, but not in the static config. Can anyone duplicate this?

I can totally live with no YouTube. The Netflix one is a harder pill since we use that ALL the time.

Thoughts? Am I missing something obvious? Thanks!