This is different than a permanent rate buy-down, because you get more buying power to achieve a lower rate.The goal would be to refinance after 2 years (which rates should decrease in that time period if you bought today).This strategy is used for traditional financing, but obviously you can to do "sub-to or seller finance" to achieve great results as well. 

Verse long term hold/rental, where you use this short term money to get the property up and running, and then secure permanent capital with a refi at a lower interest rate to cash out the investor.Also what's the investor looking for, out of funding your deals?

I'm not sure what you are referring to on "trailers" but if they're movable, and not attached to a permanent foundation, forget it.

I would definitely recommend waiting until after you settle in to your permanent home area.

Paid cash for the land, interest only on construction note, closed on permanent financing at completion with land as down payment/equity.

The landlord seeks in good faith to substantially remodel the dwelling in order to permanently convert it to a commercial use, or to personally make permanent use of the premises for non-residential purposes, or to withdraw the premises from the rental market altogether, with no intent to sell it as housing.If landlord does not comply with these requirements for notice to tenant, he will not be entitled to recover possession of the premises until proper notice is given.Read the law: Baltimore City Code of Public Local Laws, Article 4, § 9-14 and 9-20

Ideally, I would like to house hack, but instead of living there permanently, use one half of the duplex for a summer "vacation home" for when I return from overseas for leave.

Even then it will have to be a certain age and need a permanent foundation to even start to qualify for traditional financing; some lenders won't finance unless it's in it's first and original location.

I wouldn't bet on getting a re-finance if this is your exit strategy so be careful and go talk to as many lenders as you can and find out what their requirements for a rental property refi and try to get a solid commitment to refi it when ready to do so.I will definitely speak to some lenders now that this seems like a more permanent deal.

....get fat