If water gets into campers it can be difficult to remediate.

Unfortunately, you will have to remedy this situation now.

John, I own a mold remediation company so to CYA let me preface this with a " if you have concerns you should hire a professional certified and/or licensed in mold remediation." 

I have only seen one person that did an inspection and he did it with the intention of remediating the issue when he found it (he did).Also, if you're in an As-Is contract, you should have an inspection period built in where you can walk for any reason. 

My goal with purchasing the restoration business was to get closer to forced appreciation units and use my own crews to do the mold/water/fire remediation work on destressed properties.  

Telling a guest that they are paying less to put up with an inconvenience will just highlight the inconvenience and does little to remedy the annoyance.

My main concession would be the cost to remediate mold issues.

Almost if not all failed portions of your inspection report need to be remedied completely by the seller before closing.

In either case, the remedy to market knowledge is talking to more investors and RE professionals (PMs, agents, even contractors can be a great source of info) in your market as well as reading whatever information you can on the areas.

Learn about remediation of cat piss,.. trust me, it’s a horrible experience but totally doable.