So who knows what the localities will and won’t be able to choose on their own later on.  

The property will last forever, but if rates go down, you can always refinance later.

Hopefully sooner rather than later lol

The trade-off is losing out on potential growth from a reinvested 1031 exchange, but if you’re thinking about a HELOC later to invest again, this could bridge the gap.What I’d do in your shoes:If it were me, I’d run the numbers on a worst-case scenario for each option.

I used a LOC to build a 12 site RV park in a small town, opened it up and 1.5 mnths later, I'm full occupancy and servicing the debt (some of it at 8.75%) & cash flowing.

Either way, there is nothing you need to do - now or later.

I just don't want to be stuck with a high APR or MIP later down the line.

Perhaps you can barter that for experience and, perhaps, a taste of the profits and then, later when you're capitalized, do what you're suggesting but now with experience and skin in the game.

I’m leaning towards the Fannie Mae route but have no idea the process to transfer it to your LLC later.

Available but not on demand.The Lowballer: Initially quotes a very low price but may later demand significant cost overruns.Be wary of contractors who become defensive when you ask detailed questions.Happy hunting!