When there are a lot of vacation properties for renters to choose from and there's more supply than demand, you have only two ways to make money... stand out because you're the cheapest or stand out because you're the best. 

What’s true in one area may not be the same in another.That being said demand is outpacing supply in a lot of areas mostly major markets experiencing rapid job and population growth.

And more parks close then open so the supply is shrinking.  

During my research, the best STRs are the ones that own a dock but that's very expensive & limited supply.

It's one of the reasons why I've not done one since 1999.Suppliers:Always provide the supplies for your buildings, never let your GC pick them up. 

The basement being finished in general and some extra space should increase the value as well.I plan on paying for an appraisal to get the as-is value and also supply the appraiser with my scope of work so that they can give me an estimated ARV.

Every season from September-May I live in a league supplied house somewhere in the Midwest (from Jersey) and referee hockey.

Lastly, you could study permit data to get a better idea of how the relationship between supply and demand is trending in your target market. 

This will give you an idea of market rates for entertainment, supply, penetration % assumptions, etc.

Well, how much are you Capable of buying.