Many thanks to both ClutchD and hbillsmith and their previous thread on this topic. I couldn't reply to the original as it's too old, but it helped me immensely.
Here's the link to the thread.
I followed their instructions "to the letter" from both ClutchD and HillBillSmith , yet could not get the Champion 3400 inverter genny to fire up on propane.Went so far as to make sure my QuickConnect BBQ would fire up and did without issue.
Fifth-wheel trailer is a 2017 Rockwood with the barbecue quick connect off of the factory regulators and (2) propane bottles, so my frustration and disappointment levels were starting to ramp up...
Took one last long look at hbillsmith's picture diagram...ding, ding, ding...
I had the large Safety Valve end of the hose plugged into the generator.
When I switched it around and plugged the Safety Valve into the trailer quick connect , now further away from the Champion generator, she fired right up.
-sigh- all is good in the universe again
So now I think I'm going to go with this 12ft connector hose to give me a bit more distance from the trailer.
https://www.amazon.com/DOZYANT-Press.../dp/B06XK43NL3