Wow. This would be a tough one. This investor basically has all the leverage and the park owner has none. Any attempt to raise rent will be thwarted by the mere threat of him pulling out all his homes. In fact, you may buy this and on day 1 he could insist on a rent decrease or he gets a crew to start loading homes up.
Another big problem is financing. Unless the seller will carry this I can’t see how you’d get a bank to commit. The only way I’d consider this would be if I could buy at a screaming price (read: minimum 15+ cap) with very little down (~5-10%) seller carry.
Best of luck! Let us know what happens.