How do you convince someone? Basic sales tactics.
First you have to understand his reluctance to stay offsite. Have you asked him why he only stays onsite? Hard to convince someone if you don't understand what the barriers or motivations are in the first place. Ask the question, and probe for the whole truth, but don't try to argue at this point.
Once you understand the barriers/phobias/misconceptions or any other reasons, then you need to walk away and spend a bit of time to figure out your approach. Sales people don't do this step, they generally already have tactics to overcome barriers and have been honing them for a long time; you probably don't have the luxury to think of every argument, so don't.
Once you have figured out how best to rebut his arguments for staying onsite, have a calm rational conversation about his reluctance and educate him on the many benefits of offsite.
There are really only a handful of reasons we regularly see here in the this forum:
- Convenience of staying onsite; all-in-one planning and the Disney "bubble", the stinky sweaty buses.
- Perks of staying onsite; EMH, 60 Day FP, DP etc.
- Perceived luxury of staying onsite; expensive must be better
There are many, many threads here that discuss these reasons and provide rebuttals. But at the end of the day, since he is Dad, it may just be "my vacation, my rules" if he is paying.