On Board Generator vs Portable Generator

We plan to be on the road for a year or more. So we will be camping/traveling in all temperature extremes. It sounds like the best way to go is to have a built in Onan, and a portable generator too. But, storage will be a factor, so it has to be one or the other for us. The Toy Hauler(s) we are looking at are max 28' overall. To help with battery charging, we will definitely be getting a solar panel. Were also going to get a cab high truck bed shell, I have a wood framed raised bed for it. Its great when you want to leave your trailer behind and use your 4x4 truck to get back in the hills and camp out for a few days.
colliehauler, I looked at the TH forum first, but it didn't seem very active. But, I'll take your suggestion and post the question there and see if I can get any valuable feedback, thanks.