You can refinance into a FHA 203k or like @Jason Wray mentioned you could even use a Fannie May homestyle renovation loan as well!  

@Robin Simon I completed a refinance with my credit union at terms of 3/30/75 @6.85% I will have the renwal in 2026 and hoping rates come down a little by then.

Then once you've fixed the property up and at least have it listed for rent you could refinance into a DSCR loan.

I might be able to help, but what's the reason your builder is looking to refinance? 

I can help with the refinance to pull equity out, but no the purchase, as 99% of the industry won't finance mobile homes. 

Personally, I'd cash-out refinance into a 30 or 15 year loan.

Usually of the home requires major repairs it may require a HML "hard money loan" then you refinance in 6 months on the new ARV.DSCR is also not a great avenue for low loan amounts because all loans under $125K will take a rate hit and the minimums are usually $125k after down payment with some going down to $100K Min.

What you use is what you have to pay back.Cash-Out Refinance Cash-out refinance this gives you cash from the equity you have built up in your home.

Another great option is the BRRRR method (Buy, Rehab, Rent, Refinance, Repeat), where you buy a fixer-upper, renovate it, rent it out, and refinance to pull your cash back for the next deal, and this is a good route because most private lenders can go higher LTV than on a rental loan! 

Just underwrite a refinance assuming about 30-36% of the money you will receive goes to refinance closing costs at worst, and find discounts when you can.