Start with Zillow and it automatically goes on Trulia and hot pads.

He seems to be under the assumption that it would cost 12k per lot just for bringing in Power, Water and a concrete pad.

They may be trying to pad their profit.

Guests ended up trying multiple times and sometimes the pads would just not respond for a few minutes and then suddenly re-activate and let them in.

"Just for fun" examples are prohibited here, but you can find what you want to see in a couple of mouse clicks. 

I would like to put a garage or parking pad at the rear of a property in Baltimore City however there is a support cable from a utility pole blocking access.

Those locations tend to be more profitable and they could be planning a move to a pad location somewhere nearby.

Common areas are furnished, personal locks on every bedroom, key padded front door, clearly labeled kitchen cabinets and fridge shelf for each resident, etc.

Use other services too,  Craigslist, Trulia, Pads, Whatever. 

If you have a new property to rent or leases coming up for renewal ask them to sign multi year contracts, you will save on repairs and the expense of getting your pad ready for the next renter.