My next camping trip is to Senator Wash CA (10/1-10/5) which has dust issues from the drive in as well as the high potential of blowing sand/dust when camping.
The dirt road (one way) is only around 2 miles and expect to travel it 2-4 times.
I will not have shore power, so any use of AC will be limited.  
I have been working/thinking/planning a potential vent closing solution which could involve not climbing under the T@G. 
The travel issue I have run into is unexpected dirt roads. 
The major sources of dust entry I have identified may be the vent under my deck 16" x 4", cowbell AC vents on the side of the T@G and the vent under my refrigerator.
I have included some diagrams of some of my solution thoughts. 
My solution would be closing all the vents when traveling. 
PLAN ONE would be using self-closing hinges and a thin cable.
The system would be normally closed and opened at a campsite as necessary. 
PLAN TWO is the same type of system using some sort of slide rails and a spring to keep the system normally closed. 
I believe both have potential and should not be too much impacted by rough roads, wind or water.
Planned material I would use would be rust resistant and with the use of a support plate, should withstand the forces involve with self-closing hinges and/or spring(s). 
For the back galley vent under my refrigerator, I should be able to simply cover it from the inside by sliding open the refrigerator tray. Even a small mat should work for this issue. The dust issue here is mainly limited to the galley area.
The exterior chrome cowbells on the outside will be blocked with a cutoff pool noodle with some light cord stung through in the middle to facilitate pulling them out. I will carry some extra "cowbell stops" in the event I lose one or two.  
Blocking those four points of dust entry should go a long way at eliminating the major dust issues encountered during offroad travel.
Below are some photos showing what I am working with. 
 Comments are welcome. - Thanks   
Current Under T@G layout
  PLAN ONE self-closing hinges
 PLAN TWO spring rail
 Senator Wash CA dirt road
 Under T@G current


                  
                
Comments
The dirt road was closed due to recent monsoon rains.
I unhooked and attempted four times, but my Toyota RAV4 did not have the ground clearance for my comfort, let alone towing my T@G.
A new major find or oversight discovered was a 10" x 10" wood cover on the interior of my 2018 T@G under the air conditioner. I assume that nuCamp made this opening and panel to install the air conditioner air flow fan.
I removed that panel today and confirmed that it holds the small 12-volt 2.0-Watt fan (SUNON MagLev ME92251V1-000U-A99) which you manually activate when you run the air conditioner.
The opening appears to be a factory afterthought. (hole cut with rounded corners), but it was attached using two Phillips head screws.
About 9 inches down in the opening between the walls was the 4" x 16" screened vent.
The back side of the vent area has around 2" of base wood, which could be utilized to install some self- closing hinges, if desired to fashion a close down to the vent.
Having the ability to close the vent from the interior of the T@G could be a game changer to my plans.