I purchased a hand POL to hand POL with 350psi rated hose.

Project was to fill my 5 pounder from my 30 pounder.
///first phase of testing///
Both tanks set outside in shaded area of about 76 degrees.

Tested at same temp

Connected hose
Opened 5 pound valve
Opened 30 pound valve
For about 1 minute I could detect flow.
Opened overfill port on 5 pounder.
With hand on side of tank I could feel an approximate level but no further
flow to the tank was detected.

Closed valves and purged hose and disconnected and weighed the 5 pounder
It had gained 2 pounds.  Less than a half fill.
////second phase of testing////
Set up for test two
Took several cooled 1 pounders and my adapter and bleed most of the propane
out of the 5 pound into the disposables. And weighed tank to confirm the
TARE weight plus .5 pound

Test two
Cooled 5 pound thoroughly in fridge and then set in some ice water.
Reconnected everything and began fill again.  Fill sounds were much louder
and ran a bit over one minute.  Disconnected and weighed.  Weighed in at 15
pounds or TARE plus 4.5 pounds for a full tank.

/////
The results of this as they would pertain to the westy tank are.

You could use such a hose to connect a BBQ style tank to your westy tank and
then open both valves on vapor-upright and not tipped for liquid.  This
would send pressurized vapor into the westy tank which could then go through
the regulator into your van's gas system.  This is the same principal as the
extend-a-stay used for other RV.  The tank doesn�t get used to fill the RV
system only supplement it.

It would not be feasible to use it as a filler as I estimate only about 2
lbs are going to get into the system.  However 2 lbs can be a day or day and
a half.

jimt