Thanks for all the tips, serious or not! One of the most elegant suggestions presented in another dust thread "Big dust coming in the back doors" was purchasing the inner gasket for the side doors, cutting it in two and installing it on the sides of the rear doors. It appears to me that same door seal could also be applied to the driver side rear door where it meets the passenger side door. However, I came up with four other changes for my particular van before trying the additional gasketing on the rear doors. These were 1) rear door hinges, 2) side doors, 3) battery cases and 4) Propex heater.
First, I attacked the rear door hinges. I was motivated by the report above of dust coming through the rear door speaker cutout and my own observation that in one rear door that SMB made into a storage compartment, there was lots of dust inside. For that to happen there has to be a flow of dusty air from some inlet(s) to some outlet(s). Aside from drain holes, which should not be sealed, I noticed that the two hinges on each rear door had gaps around them (left photo) while the side doors have a gasket sealing the hinge gaps (right photo):
So I used waterproof metal repair tape by Nashua purchased at Home Depot. The tape has a backing that needs to be pulled off before applying, which makes it ideal for sealing those areas. I first cut lengths of tape and folded them with the backing facing out on short pieces of old venitian blind blades. I then trimmed the width for the piece that goes on the backside of these hinges and with the help of the venitian blind strips, I applied the tape after taking off the backing. The photo below shows the venitian blind stock I used (left one is for upper hinge and right one is for lower hinge):
The next problem was quite a bit of dust coming in through the bottom of the side doors even though they seem to close tightly. Those doors are already double gasketed on top and sides, but there is only one gasket on the bottom, i.e. on the door itself. So the only thing I could think of was foam tape on the door upholstery of both doors so it contacts the black plastic step.
The next problem area was the battery boxes. I chose to have the (three) house batteries installed inside the van thinking that would result in better performance for winter camping. What I did not realize is that each battery would be placed in a separate battery case with each case vented through the side of the van and also through the floor with holes you could drive a tractor through. Why this was done for sealed AGM batteries I have no idea.
Further, the battery cases were not sealed and the battery cabinet door was entirely worthless for keeping dust from getting getting everywhere else in the van.
To fix these problems I put a sheet of plastic between each of the three chrome vent covers on the outside of the van and the through-wall gasket to seal the air vents. I then plugged the drain holes from the inside with 1" rubber furniture feet, placed upside down in the tapered holes (great fit), and sealed them with Sikaflex 291.
The last fix had to do with the furnace. A Propex heater was installed under a bench seat by Van Specialties in Portland, but it was not a great job. Not only did they not follow detailed drawings of exactly where to install it, they also left holes through the floor that were not sealed in any way. That avenue for dust to come into the van was accentuated by the fact that the Propex heater brackets hold it off the floor so any dust wanting to come in through the combustion air inlet and exhaust holes has an easy path into the van in a big way. With the radiator clamps on, the holes don't seem very large, but they are:
To fix this problem, I did two things. First, liking the idea of seals and backup seals, I surrounded the pair of holes from the inside of the van with foam insulation and at the same time applied Sikaflex 291 on the edges of the inlet hole and Permatex Ultra Copper High Temperature RTV Silicone Gasket Maker on the edges of the exhaust hole. Then from the underside of the van after the heater was reinstalled but before the radiator clamps were put back on, I sealed the gaps with the appropriate sealant.
These four fixes should help the dust situation. Exactly how much is not clear, but I will see how much these fixes improve things before going to the next level. Some of the above fixes may only pertain to my van, but the rear door hinge gaps should pertain to pretty much all Ford vans.
2008 E-350 6.0L diesel:
Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
4 cf fridge, nuker, water heater, compressor
stove top, furnace Travel: https://www.lugnutlife.wordpress.com