If the numbers make sense, choose quality over cutting corners and your vacancy rates will stay negligible.       

Our lending agent simply dismisses his negligence because "I didn't understand Fannie Mae's guidelines."

I would check in your local area with your (if you have one) PM company and find out what the demand for this type of appliance is and if it is negligible I would not do it.  

I also have a terrible roofer, and an HVAC guy who borders on criminally negligent.

Liability might only apply if the insured (tenant) was negligent in some act.

@James Slaughter although anyone can sue anyone for anything in the end liability falls to who is negligence don't be negligent and you won't be liable  but have reasonable limits to be safe  as you want somebody to defend you to prove your not negligent 

There are many factors to consider.As to negligent hiring that is possible but much more difficult to prove. 

@Erin N. unless you acted negligently, you are not responsible for the leak.If you lease dictates that the tenant is responsible for the bill, it's the tenants responsibility.  

Insurance and taxes on a MH are negligible, and if one sells the property on a note, maintenance isn't an issue either.

Even so, tenant comes up with BS excuses it's your negligence that caused his loss and sue.The additional insured designation would insure that the insurance company also notify you in the event he cancels the insurance.