I currently have a built in Onan LP genset. Works very well.Simple push button convenience. No cords,cables, locks,no gas tanks etc. Perfect for quick breaks and spontaneous use. WE can eat at a restaurant while traveling and leave the dog inside RV with A./C on. We can eat in the trailer with A/C and microwave 5500 Onan will run entire trailer including both A/C units.
On my prior TT I had a Robin Subaru 4300is mounted on a rear platform. This set up was not quite as convenient or powerful but worked very well. Genset was semi permanently mounted. There were no security issues. I had to plug in trailer vs. current push button start. I also had to have gasoline for the genset vs. lp which is already on board.
In the end I prefer the genset to be attached to the trailer vs.the truck. If the truck leaves the power is still with the trailer. I prefer the genset to be mounted to avoid any set up or carrying of the genset. A mounted genset is more convenient to use . It requires no preparation to use it. It can be used spontaneously without a lot of thought or set up.As a result we use more often.