I use this one (Amazon, about $30) because the probe is on the coiled cable and I can reach into tight spots and still read it. I sharpened the probes so they go easily through the vinyl floor covering into the plywood subfloor.
I probe around the interior perimeter wherever I can reach. I open the outside storage hatchess and there is a little bit of gap between the aluminum diamond plate and the inside shell; probe the plywood there. Likely spots are below entrance door sides, below windows, and below awning support arms.
This meter needle will move about half way across by touching my dry finger. If I see any movement at all probing the floor I am very suspicious of a leak. Will pull the plastic baseboard screws, lift the vinyl edge to investigate and monitor to see if it drys out in a day or two. If the needle moves more than half way there is unwanted water and I look above the area for a leak, and seal.
The other source of high moisture at the perimeter is condensation dripping down the surface or between the aluminum walls. Could be from the windows. Most likely to happen in cool, very moist or rainy weather, especially if cooking or showering. If it happens, monitor it with the meter to ensure it dries out in a couple of days, or lift the vinyl edge to help it dry. Never leave it wet for a long time.
Not much point in probing the center areas, except under the shower door and near the toilet. Watch for plumbing leaks.
A good time to probe is after a long, heavy downpour, especially wind driven. I probe once a quarter along with my other corrosion and sealant inspections and system operational checks.
Doug and Cheryl
2012 FC RB, Michelin 16, ProPride 1400
2016 Ram 1500 Laramie Crew Cab 4X4 Ecodiesel 3.92 axles
The Truth is More Important Than the Facts