I have SFHs and a few small apartment complexes, but this would be a first for me.Quick run-down:45 lots, with no room to expand18 full - 15 POH and 3 paying just lot rentPublic Utilities, proper zoning, paved streetsSmall town, around 45 minutes from any sizable town; around ~2,500 residents that are mostly blue collar, lower incomeI believe lot rent should be around $250-300 per spot once full and stabilizedCurrent asking price is around $200k, with expenses running around 35-40% of gross incomeMy initial plan would be to give all POH to the current tenants if they agree to re-sign lot leases and update all utilities and other facilities as necessary in order be prepared for additional homes being moved in.  

Condo fees can also increase at the drop of a hat or they can hit you with a special assessment to pave the parking lot, roof the building, or some other major expense.

I would like to pursue investing full time and I am slowly but surely paving the way.

So I would try a commercial 'water permeable' sealer:http://www.miracote.com/products/miragard_-_vapor_permeable_coatings_and_sealersIf that fails I would be tempted to drill a number of sump holes (to allow a larger concentrated diffusion of moisture) around the slab perimeter.

These things are usually fixable with money; you pay an electrician to put in meters, or a driveway company to do some paving, etc.After that, it's just the "normal" stuff that happens with an old house. 

I know lot rent in the small town about 10 miles away  from me is $125.00 so they do vary.The park is has city streets are 3 sides of it that are paved.  

Don't forget there will be site work as well, landscape, paving, etc.Example:   $200,000 / 2700 sf = $74 per sq ft.  

I'm also employed full time as a marketing executive in the medical device industry; real estate is a passion and pursuit but isn't my j-o-b.Near my investment properties is a 37-unit  with paved off-street parking lot, combined with a few rental houses that are adjacent to it.

Is paint vapor permeability a concern? 

The property manager said we only had space for two cars and she wouldn't allow us to have a third space paved.