Phase #1 - Recovery  - characterized by high vacancy rates and no new construction- rent, during this phase, is flat or declining- owners offer rent concessions to avoid their property occupancy rate from  decliningPhase #2 - Expansions- characterized by declining vacancy and the start of new construction- occupancy improves, concessions are not being offered, and rental rates being to growPhase #3 - Hyper Supply - characterized by new construction and vacancy rates beginning to rise - rental rates begin to grow at a slow rate- rent concession are being offerred due to the new construction in the area [in the hope of retaining current renters]Phase #4 - Recession - characterized by the completion of construction and a decline in occupancy rates - concessions are abundant to avoid high move-out rates Here are some foundational truths about optimizing your investments:#1 sow seeds of success in the down times - "The season of failure is the best time for sowing seeds of success."

As part of the project, the only existing drain on my side of the street is being sealed over with concrete and even that will be lost.

A cash purchase, added to my portfolio, reduces my levergage ratio on my real estate portfolio, but does not bring it to zero of course as I am not paying off existing low rate mortgages on rentals. 

We've heard that the leases are for 18 months, but that FEMA retains the right to cancel them with 30 days notice.

The existence of a contract -- I agree with you on this -- may be a complete defense to such a claim. 

You're increasing the need for hot and cold air dramatically and it's doubtful the existing system will be adequate.But, in answer to your original question - yes you will need a permit.

But I do have an issue with asking some of these pre-existing cabin owners to have to retrofit their cabin with the system and expecting them to have it done in a year or something. 

NOTE: A lower OER indicates a more profitable property as a larger portion of the income is retained after covering operating costs.Hope that helps!

I have a note in the lease that they're not supplied or warranted by the landlord and the extent of what I will do (if any exist at all) is haul them away. 

A lot of times it is best if the existing pm is the listing agent so they can negate this along with tenant communications.