you will be fine boon docking - campgrounds will most likely have generator use restrictions. Mostly limited to during daylight hours but some are more strict with hours around meal times.
I see no problem with what you want to do provided you don't disturb the peace if other people are present. It sounds like you have a portable unit - if its one of the honda or yamaha types then It will run pretty quite anyways and 75ft between the two of you will make it almost not even noticeable to you or many other people. If it's one of the "commercial" or "construction" types like the Champion then it will be much louder though at 75ft and a trailer with insulation between you still probably won't here it. Others might though.
Be a good neighbor and if no one is around or its far enough away then don't hesitate - it's what you bought it for!
Don't worry about the emmisions - mostly an issue for us with onboard Onans next to the master bed.
Happy camping!
