Just a few items; lumber prices are up 325%, conduit is up 50%, any product which is produced with materials from one country and assembled in a different country is taking 3x the normal lead time, at best.  

Yes, the fixed, low rate for 30 years (as opposed to the variable HELOC rate) is part of what makes the refinance an attractive option (in addition to the cash out).

I’m hoping to start off in an elite brokerage who produces the best outcomes for its associates, but I am lost how to find one?

Over a 7 year period I think it will be an attractive investment.  

Any suggestions on how to be more attractive to the lender so we can keep both? 

One thing to keep in mind if you do rent is the type of clientele the units will attract and if you're comfortable working with that type of clientele. 

If it doesn't produce positive cash flow when fully tenant occupied then I would be very hesitant to move on it.

A spread of 2.5% (5 x what they're getting today) might look very attractive, and still leaves 1% for the deal maker.  

I'm aware that RV parks are already on a faster depreciation schedule, and that's a great reason for why i am attracted to them.

You may not "need" to do these improvements, but nice units attract nice renters, crappy units attract, well, you know.