What's replacement cost? You are basically buying the replacement over time since there is nothing there for you to work with.
$10k per empty pad may seem cheap or steep (depends on how long through its useful life I suppose), but $100k for the license and $30k per occupied, seasoned, rented space at ~$350 per month (with the "manager" working for space-rent comp) seems do-able in ? 1-5 years?. Can you do the capital lifting (bring in $5k home, put $5k into it, pay other people $5k to deal with it, sell it for $30k? And not get it back? If you can do that once a month or so, you're looking at 2-5 years to fill & flip on a reasonable cap rate as an income-producing property. Put $50k down, $15k into each of 3 homes, $35k working capital ... might work or you might be upside down from the start. Would 2 rented lots (I assume your manager lives in the third one) at $500 cleared after expenses, per month, be enough to work with? Sounds doubtful.
Run your own numbers and see if it's compelling for you. You'd probably need $130k in cash to pull this off comfortably.
If the park is generating $1k per month (let's say) or about $100 per lot, at an 8-12% cap rate (reasonable range), if you invest $10k per pad now, and reap $30k per pad later, that gives you $20k per pad of potential future profit. Can you fill at $20k per pad?
When you will see this profit? Perhaps you make $15k per home (on the sale) and break even overall on the homesco 7 years out, then your park-co could be "in the money" so to speak after 3 years. You've purchased at $130k, and you finance it at 70% LTV at a value of $200k because it's generating ~?$2k per month or $200 per lot at that time (giving you back your $140k -- or whatever numbers you like here) and recoup your $130k and have $10k left over to reward yourself. Would you do all that work to risk getting the [expectation value of what you calculate] plus-or-minus [deviation] with [perceived risk]?
Plus-or-minus deviation is a big swing relative to the amount invested. It does not seem compelling. More of a speculative gamble. Try running the numbers paying $0 per pad and see if that's compelling. Probably not -- you break even on the homes (you hope!) and get the park filled with your labor and capital and in the end you have a park worth maybe $130k (generating $1k per month clear income from average of 2 vacancies clearing $100 per pad in rent each rented lot. ($100 x 10 income-generating lots x 12 months = $12,000 per year at 12% cap rate is $100,000 value.
All of this is more than the usual "quick-and-dirty" because you aren't buying an income-producing property, you're essentially building a mobile home park from scratch, but over time. So F & D's quick-and-dirty doesn't apply. And you're buying mostly land plus a license plus potential liabilities and no income. It doesn't make a compelling investment. More of a dice roll. Compare to raw land with $130k spent getting it zoned properly and you'd be in the same boat with no infrastructure, which is not completely unreasonable. Well, you're proposing to be $10k per lot ahead of that guy. Do you have any hope of expansion or combination with another park? You are essentially asking if you should pay $10k per lot to expand your current park with existing infrastructure.
I would call it a wash if it's 50% through it's useful life since a new park might cost $20k per space. Or vary your expectation and evaluate accordingly. Running the numbers and getting some handle of how realistic they are will probably lead you to pass on this, but here is a potentially compelling scenario.
The infrastructure is 20 years old and will last another 20 years. You own the adjacent tax parcel. The city is willing to let you combine the parcels, and, bonus, will deed the dividing road to you so that you have a larger contiguous parcel. Just to make matters delicious, you sweet-talk the local mayor and leading local attorney who sits on the town council, just coincidentally in your district, into agreeing with your worldview that providing decent affordable housing is a valuable civic contribution and in exchange for your plan they will tear out the road, and replace it with a public park on their own tax dollars. Then, they'll give you a tax abatement in anticipation of your accommodating another 20 potential voters and bringing economic vitality to the town. Think "It's a Wonderful Life." Also, happy New Year!