I know this forum hasn't been active for a while now, but I was looking to add Onboard Air on my 2014 Silverado 1500, and this was the first, and one of the only, forums I saw for Silverado's Onboard Air. However, I did not find a direct answer to my question...
When I switched over to 35" tires, I had no use for my stock spare, so I took it out and thought that would be an ideal place for Onboard Air, since there is ample room to work with and its all accessible. I looked all over the internet for someone who put an Onboard Air setup in the spare tire location... and all I found were kits that started at $1000 and only went higher.
I decided I would get a Viair Onboard Air kit, and make my own affordable mounting solution.
I designed a mounting system that utilizes the spare tire location and existing bracket, in which my plate and spacers are bolted to. My plate is made out of laser cut, 10 gauge (0.135" thick) 304 Stainless Steel, which is quite oversized for the overall weight of the Onboard Air system, but very high quality. Stainless allows for the plate to remain unfinished and not have the ability to rust.
I attached a few pictures of my overall setup (pressure gauge, switch, and air quick disconnect may be located wherever you choose). Hopefully this helps more people, like me, who were looking for different options or something more affordable.
If anyone is interested in replicating my setup, I can make a video or write a How-To on my process for installing and routing all the wiring.
Please send me a direct message if you're interested in buying a mounting plate, they are cheap and become even cheaper if there's a large order! I can also modify it or make a custom layout if you have your own mounting solution!
*The Onboard Air System used is Viair PN 20002, but the mounting plate works for many other Viair systems*