I would have put it where you put your house, but since that's not an option, I'd probably put it right next to the train station. There's not really a good spot for it lol
spot two. my town map is different but i have my camping area in between the railroad tracks and river in a small piece of land like that and i love it.
I like spot 2 as well, you can always try and see if Isabelle will let you build it there with the villager house as it is (doubtful) - or how about the other side of those two houses (ie still along side the railway tracks but closer to the train station).
You can get Isabelle out & try locations and then just say no cancel the project - I do that to see if tight spaces are possible (I've sometimes been pleasantly surprised at what I can squeeze in).
If you go to the point of fixing it with Loid there - you can still cancel (just don't pay any donations towards it, cos you would lose those if you did).
The only downside to this is that is it for the day - you can't build another PWP that day.
The other advice I would give - if you are going to be using the campsite for getting in villagers then I would place it along a pathway route - if you put it in an out of way place you could forget to check it.