RVs are required to be tested to a min. of 100 psi. I found the regulation a few months ago but can't find it at the moment. If anything leaks it's the result of defective workmanship in the factory. If I would suspect anything, it would be the "swivel" fitting connections to the toilet and faucets as these are hand tightened. Two regulators in series won't regulate any better but perhaps *could* help if one failed (to regulate). But, the exterior inline ones have a tiny orifice which can easily plug up from sediment and severely restrict flow and is the usual failure.
PEX fittings cannot possibly loosen over time if they were properly installed. They don't normally use crimp rings, which are made from copper. Pex is usually connected using a cinch clamp. Both a ring and a clamp require the use of a special tool and both are calibrated to ensure the correct pressure when tightened. There is no need to go through an RV and replace fittings with Sharkbite ones. I supposed one could use a cinch clamp tool and check existing clamps. There's no clear answer among plumbing professionals if a clamp or ring is better. I find it hard to believe that copper would be cheaper to install in a house as it's so easy to pull PEX through holes in studs and joists and 90 degree bends can often be avoided. When I was still working in construction, everyone was using PEX in wood frame buildings.
The problem with RV plumbing systems, as well as electrical, is that the factories don't use qualified tradespeople and the work does not get inspected. Our new TT came from the dealer with a kinked PEX line to the bathroom that was 100 percent blocked. A pressure test would not have found this and a test of faucets should have picked this up.
CG/RV park city water pressure can sometimes exceed 100 psi. I installed a recording type gauge and have seen the pressure up to 140 psi so far. Some have reported it getting as high as 200 psi. It is a bad idea not to use a regulator. Pressure can go up overnight sometimes with few users compared to the daytime and you can't be there to watch a gauge overnight.
I installed a Watts regulator under the kitchen sink near the city water inlet. All piping between the regulator and city water inlet (incl. the inlet) are brass and can withstand high pressure. Hose to the CG faucet is a high pressure type. Removed the cheapo check valve in the city water inlet and installed a good brass one. Upon the recommendation of the owner of RVwaterfilterstore.com, I have our regulator set at 65 psi.
I don't like the basic/cheapo/entry level inline exterior regulators. We bought one in the beginning and it failed in under one season.
A plumbing component that could be the most likely to fail is a toilet valve as the owner of the fifth wheel in this vid found out.
RV horror story. I installed a main shutoff valve inside so that we can shut off the water if away for any length of time. Toilet valves are really cheap devices and I need to replace ours due to leaking and that's after only 2 seasons.