Tire inflation

I would also worry about getting sand between tire and wheel possibly causing air leakage, sand in exposed tire valves might also lead to problems.

Personally, if you are required (or need) to air down to drive on the beach, then I would not take the chance of driving an RV on the beach. Hard packed sand that does not require air down, sure. But not in soft sand. You are looking to get stuck with that weight and no 4x4.

Good day
18 psi is fine for the beach.
at 5 MPH your tires will not come off of the rims.

There are usually 100000 opinions on tires. Look, stay within 5psi of MFG suggestion psi. I would not deflate for beach or anywhere else.

Check out the truck camper forum. Those guys are much more knowledgeable on off-road travel than the answers you are receiving here. They carry a lot of weight on their duallys, too.

The tires will not stay on the rims at 18 psi so it wont matter which one you try to inflate first. You should never run the tires under inflated or you will damage the sidewalls. You may get away with it on a car because 18 psi may only be 10 psi under normal, still not good but on an RV you are talking 50 psi under normal.

18 psi seems very low considering the weight of the motorhome. 18 is fine for my 4Runner, but it weighs a lot less than my motorhome.

Are you not concerned about flats from duals bumping against one another?

Thanks for the reply. We drive on the soft sand no pavement or hard pan. Need to have lower tire pressure or the rig will bog down and get stuck.

And yes the rig will get a nice bath on Sundays to wash away the sand and salt.

I would never decrease to that level or even close to that. You have the potential to flatten one or more of your dual mounted tires. You tires can bump against each other knocking loose from the rims. Instant flat!