Refinance offers a lower rate, longer term and a lower payment.

I don't know your specific market all that well but have you done some analysis on your ADR during the high season X your high season occupancy rate and determined whether taking lower priced slow season bookings vs letting your property stay vacant during the winter averages out in your favor?

.- get into real estate with a lower rate and lesser percentage down payment.

You can get some insurance on unpermitted units, a lower coverage amount than for a permitted unit and will have difficulty rebuilding it as a permitted unit at the covered amount (which makes sense because its value is less than a permitted unit).  

Giving away the place cheap only creates more work for yourself screening lower income individuals, and attracts scammers.

Are costs really lower with a container? 

Getting it under market value would be a bonus.So, would using an FHA 203k renovation loan, which would allow me to buy something unqualified for a standard mortgage, which would weed out a lot of competition and push the price lower.

I’ve had several investor clients go with a new (to me)/ unproven lender because of a slightly lower rate promise only to get burned by that lender (closing costs were higher, appraisal costs much higher and appraisal was a nightmare, main point of contact gave us the clear to close as we passed our financing contingency then just before closing someone from the underwriting department we previously didn’t know existed said we need a few more days and seller didn’t agree because they had a higher backup offer, jeopardizing the earnest money and losing the property, etc).

You can get away with using 5% for Class A tenants, but we use 10% for Class B and lower. 3) Tenant Payment Performance: you didn't mention this, but it is important!

The first question is, can I use a second home mortgage (10% down and lower interest rate) for this.