I live in French Valley (Murrieta/Winchester), a few miles from you. 

We install a french drainage system all around the house and get talked into raising the concrete in the house by about 5 inches.

i know a lot o you are not hands on with your properties, but I for one, am, the sewer lateral issue has been a big one for me, so i purchased a 50 foot USB drain camera on Ebay for $15 or $20 attach it to my electrical fish tape, and inspect the line as part of my rehab, or prior to purchasing if possible. it works for me.

He might be a good LO to connect with. 

You're not in the French Quarter, so you may not be able to be quite as uninhibited, but you'll see how a bit of bold color can a tremendous amount of personality and character to a tiny house.Let me know if you need any more suggestions.

Then we installed a top level french drain below the frost line.  

For basement units (I'm assuming that one of the units is in the basement) I'd want to carefully look to see what the water issues are down there: is there a french drain or other system?

Larry French runs a club in Coachella Valley.There is tons of houses and opportunity here.  

Main components of rehab were:New windowsRefaced cabinetsNew rear doorNew french doorPaint interiorNew counter topsAll new floor coveringsUpdated all electrical finishesExterior paintedNew gutters (First time we used black and think it turned out really nice.)Graded a new gravel drive.This was the first time I attempted to use a GC.  

Sump pump and several french drains further helped.