Tim, if all else fails...
Boat drinks
By: jimmy buffett 1979
Boys in the band ordered boat drinks
Visitors scored on the home rink
Everything seems to be wrong
Lately, newspaper mentioned cheap air fare
I gotta to fly to saint somewhere
Im close to bodily harm
Twenty degrees and the hockey games on
Nobody cares they are way too far gone
Screamin boat drinks, something to keep em all warm
This mornin, I shot six holes in my freezer
I think I got cabin fever
Somebody sound the alarm
Id like to go where the pace of lifes slow
Could you beam me somewhere mr. scott?
Any ol place here on earth or in space
You pick the century and Ill pick the spot
Oh I know, (I know)
I should be leaving this climate
I got a verse but cant rhyme it
I gotta go where its warm
Boat drinks
Waitress I need two more boat drinks
Then Im headin south fore my dream shrinks
I gotta go where its warm (I gotta go where its warm)
I gotta go where its warm (I gotta go where its warm)
I gotta go where its warm!
I gotta go where there aint any snow
Where there aint any blow
cause my fin sinks so low
I gotta go where its warm
Tim...forth verse seems to be one answer to your problem...
Wow, you've got a bundle of things going on with your cooler/warmer...
To my way of thinking, if it works when stationary, it should work when on the road...so, I'd really check around for something that's disturbing the burner or flame propagation...or disturbing the proper airflow up and over the coils...do you have any unusual fixtures on the roof, around the frig vent that might be screwing up the 'normal' venting process??? Have you checked to see if you have a big mud wasp nest inside the roof vent??? I found one in ours when we first bought it - it was blocking almost half of the vent!!! Just some thoughts...
Road 'bounce' should promote proper gas/fluid flow through the cooling system - provided the burner/flue is working properly...again, that's where I'd concentrate my 'search'...burner airflow when moving...
I also don't think the axles are a contributing factor...our 28 footer has it's original frig that works really great, on, off, the road or upside down, maybe...AND I've put those same #3500 new axles on our rig last year - and in fact, the 'ride' is much 'easier' when compared with the old 'stiff' axles...in about five trips on the new axles, I haven't noticed any evidence of 'motion sickness' in the AS's construction - loose rivets, etc...
I bought one of those fiberglass 'funnel' shaped manifolds that you mount over the upper coils - and has a muffin fan in the top that's controlled by a thermostat...As you have to remove the frig to mount this rig, and the frig continues to work great, I haven't made the effort yet to install it! However, it does look like a good way to improve the air flow in an Airstream's cramped ventilation quarters...a project for a future date...!
Good luck on your mystery...let us know when you solve it...