I'm currently having a momentum 381m-R built and decided against the generator regardless of supply issues. Several reasons behind this decision:
1) Going to be full timing in it so will be plugged in majority of time.
2) With the tow vehicle I will be using I would prefer to save 300+ lbs hitch weight, also I like ability to distribute my weight where I want it (with portable gen I can do this)
3) After researching I found how inefficient the onan (and all generators) are when they are operated at demand levels much lower than their peak output. The majority of time i would run the gen just to charge my batteries, i plan to have around six battleborns (or equivalent) which would take around 3Kw for a few hours (assuming they are close to dead) to charge. With at least 500 watts coming from my 1Kw solar array I'd only be using half the onan's output. The penalty for this is consuming at least 40% more fuel per Kw generated. I would much rather plug in my Honda 2200i, getting max efficiency because I'm using 100% of its power.
4) Noise. Onans are loud. Compare the data sheets of the Honda portable units with the onan. You will find the onans are around 10 decibels louder. Your neighbors (and yourself) will not appreciate that. Of course when they test the onans they don't factor in the structure they are housed in for noise reduction but go stand somewhere facing the exhaust pipe of a trailer with the 5500 onan, now go stand exhaust side of a paralleled set of Honda 2200's. No contest. Plus, portable units can be positioned away from camp to further lower noise impact.
5) cheaper / easier to maintain a Honda generator, easier to find someone that can work on them / get replacement parts for them.
Of course the convenience thing of having the built in generator is nice but honestly even if its summer and I'm boondocking, I'd rather parallel a set of Honda 2200i's together. I can still run two of my 3 ac's and with the extended run fuel tanks you can run, some measure of convenience is regained and I still prefer portable.
I also like the ability of using the generator on it's own without needing to be tied to the trailer such as remote projects, entertaining at a remote picnic, luxury tent camping, etc.
Anyways, hopefully this insight helps someone else like me that was on the fence with the generator option (even though it may not be an option with current supply chain). Oh by the way, with 1 or 2 Honda 2200i's you will save at least $3000 - $4000 off the onan option as well