all 4 tires, no such kit exists, that is a major modification to the RV, and may not be the best thing for you.
With tires, epically the rear ones, it is important they all present the same RADIUS (and by that I mean the distance from the center of the axel to the road surface) and that may require the right and left side be different pressures.
Cross-Fire dual tire inflation/monitors http://www.myerstiresupply.com/shop/shopexd.asp?id=746
May be what you are looking for, they come in assorted pressures, I am unable to install on my coach.
Why would a "All 4" System be all but inmpossible,, Well, the side to side crossover needs rotating seals, and there is not a practical way to do that less you drill out the length of the axles.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times