I don't think upkeep on your home is business expense either.

For interest and property taxes to be deductible, a second home must have sleeping, cooking, and toilet facilities permanently installed.

I have met the requirements. As for the slip fee, I thought that if one owned a manufactured home that was on leased or rented land in a trailer park the land portion was deductible, hence the question about the slip fee??

The slip fee would not be deductible.  Nor is leased or rented land in a trailer park.  
Some states apply a personal property tax to a mobile home or boat.  That is deductible as an itemized deduction.  The tax must be based solely on the value of the property to be allowed.

Ok, how bout this !? The boat is located 100 miles from my primary home and I travel to that location for work. Can I deduct slip fees, maintenance, etc as a business expense ? 

Commuting expenses to go to work are NEVER deductible.

It’s business travel ! I’m a 1099 independent contractor 

Doesn't matter.---Commuting to and from work is still not deductible even if you are an independent contractor.  Mileage you travel WHEN you are working is a different story.  Just driving to work  or from work is not deductible.

 

And....the slip fees and boat maintenance are still personal expenses, same as if you had a house and had to fix the roof or pay a homeowners association fee.