If theres a foundation issue, roof problem and it costs 50k to fix, do you still want to go through?

You may need a building permit if only to put the units on a foundation and pave a driveway/parking lot to them, run power, etc.

Dealing with an old river rock crumbly foundation in a full cement basement.

Hello,Wondering if any of you investors who flip MH's on land for cash or on owning financing/rent to own go to the trouble/expense of converting them to a permanent foundation if they are currently not on one. 

YES install a heavy mill plastic vapor barrier between foundation walls and insulation

Even if you're doing a gut renovation right down to the studs, you should still have inspections for the foundation, water quality (especially if on a well), septic, radon, etc. 

We discovered a lot of damage from foundation movement on that side.

Roof condition, mechanical condition, plumbing issues, appliances, foundation, structure, overall flow and usefulness of layout and spaces.  

That sounds like a solid foundation on how get started.

I've been absorbing a ton of information on RE to help with foundational knowledge.