As far as PadSplit, you'll have to check city and county laws concerning the number of unrelated people allowed to live in a house. 

Also concerning, I just looked at zillow post and the pictures are very grainy and unflattering, even though they should have access to the nicer photos (I have had these for years, see below)..I've also been getting lots of calls form companies wanting me to sell my house.

Stick to the facts and ask clarifying questions to understand their concerns to resolve this.

He was an older gentleman relocating for work, and his biggest concern wasn’t price—it was speed.

Seeing that you are moving for job reasons, I would probably suggest option 4 until you learn if Seattle is going to be a permanent answer.

They can then proceed with a 1031 exchange for their rental properties.I understand their concern about the 180-day timeline.

As far as your concern about WA being a more tenant friendly state, I hear you.

One of my concerns is that lenders won't lend to potential buyers because it is a modular home.

This can provide a better depreciation benefit than traditional STR real estate.If permanently affixed to land, it qualifies for real estate depreciation (27.5 years for residential properties).Considerations:Zoning laws and campground restrictions may impact legality.Self-employment tax risk arises if you provide substantial guest services.Vacation home rules apply if personal use exceeds 14 days or 10% of rental days, limiting deductions.Audit risk is high, so keep detailed records of participation, expenses, and rental operations.Given the potential tax benefits and complexities, consulting a real estate tax professional is advised to ensure compliance and maximize deductions.This post does not create a CPA-Client relationship.

I should also note that the project would be ground up and the FHA loan would be a one-close construction to a permanent mortgage