Another option might be to hire someone off of Craigslist to take a quick drive through video of the park. I normally pay $50-75 for this:
Drive through video (Two passes) Pass one should be a front view showing all roads. Pass two is a side view showing all homes
At least 10 pictures of the nicest things you see
At least 10 pictures of the junkiest things you see
I instruct the person to do everything from their car to ensure they don't disturb the tenants or cause issues with the owner. I also tell the owner that we are doing this (not ask). If I have the park under contract then the person I hire is free to get out of the car and do their photos.
Assuming you have a layout of the park and know which homes are park owned, the video should allow you to roughly determine the era, exterior condition, and size.