Poor man's leak detector

As I've said on here before, I'm a worry wart when it comes to water intrusion. I have read a good bit about the Sealtech system, where they pressurize the RV, then spray soap water and look for bubbles. I tried a diy and it seemed to work. I cut a piece of cardboard to fit in the passenger's window and hooked my leaf blower and shop vac through the cardboard. I also ran the tube for a manometer through the cardboard. I taped up the plumbing drains, the stove vent, and had to tape up the exterior door for the shore power cord. I got 3/10's of an inch on the manometer. In hindsight, I should have checked the cab ventilation system to be sure it was in the recirc mode. Anyway, it seemed to work well. I found two windows leaking. One was at the bottom of the emergency exit, and the other was where Hehr shorted the gasket at a sliding window. Not worried about the exit leak,as it's just above the drain. I will put a dab of sealer on the other. It was a pain in the butt to remove the vent covers, but I needed to check the Dicor caulking anyway. Good news is no other leaks anywhere. I would recommend a Sealtech check, or at least a diy of the Sealtech check to find leaks. It took about three hours, and that includes R&R of the vent covers and doing the cardboard window.

Very interesting write up. Very resourceful. My grandson did similar diy leak check on his fifth wheel. Found leak about 10? away from were it was entering inside.

Here was my setup. Old furnace blower on a vent with the cover off.

I wonder if a reversable Fantasticc Fan on INTAKE would generate enough pressure?

I would imagine that would depend on how air tight the RV is.

John From Detroit said:

I wonder if a reversable Fantasticc Fan on INTAKE would generate enough pressure?

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I've had the same thought just about every time I read something about this sort of leak test....

Just a guess on my part...but I'm doubtful.  The blade is a rather loose fit in the shroud which would allow a tremendous back flow.  Also, the volume may likely not be enough to overcome all the little leaks that are of no interest for this purpose....  I figure if you did a very thorough job of sealing off the plumbing vents, dash HVAC vents, etc... then it would almost certainly pressurize it some.... but I recon it would be like trying to find an extremely slow pinhole leak in an air mattress..... like with one little bubble every minute or so. Just spraying the soapy water on will generate a certain amount of "surface bubbles" that give sort of a false-positive and make it a real snickerdoodle to find the real leaks, if any. 
I've tried to find very slow leaks in tire stems and lots of other things with soapy water with mixed results.  I figure with the very small pressure differential that I'm guessing a small fan would produce, it would probably be similar.  I only seem to have any luck when the leaks are...well, fairly substantial.

The other thought I have about pressure tests are that it's a different sort of thing...air vs water.....flowing out vs in..... under pressure vs zero or near zero pressure. 
I think about it like a house.... especially an older one.  It may be completely leak free and dry as a bone....from rain coming in....  and for all practical purposes it could even be draft free....but if you were to put air pressure, from the inside or out, it would leak like a screen door.  Not to discount the test completely though, because you can always make a judgement about each leak you find if it's an issue or not.