In MY Opinion..
The onboards are designed basically for that purpose.. Get to a stop, press a button and start the generator. the next morning all you have to do is bring in slides, turn everything off, including he generator and hook up and go.
They do get Thirsty though, depending on the load, and bottle size you will need a fill up. and EXPENSIVE.. I paid I believe $5k 5 or 6 years ago for my 6.5 Onan.
The portables are good to use for longer stops, by the time you get there, get all set up and pull the generator out, hook up the anaconda.
I used 2 Honda's for years until I got my onboard.
It will come down to if you can justify the expense of the onboard.