In that case, a premium can help discourage back-to-back bookings or at least bring in more revenue that could help with operational costs....While a premiumcan be put in place so that adjacent days are less attractive to guests, there's no guarantee that guests won't book these days, and your regular listing maximum price will still be in effect (though that can be adjusted with Date Specific Overrides).

Pete is tough.First, I would adjust your mindset.

They were quick to pay when repairs had to be done and their in-house adjusters were on point.  

I'd love to hear about your experiences and see whether my expectations just needs to be adjusted.

Just because you don't make any money on them, doesn't mean you aren't responsible, along with the source of the actual plans, for any mistakes in the plans, or even any mistakes in construction from lack of info, misunderstanding, or just plain stupidity of the builder/user of the plans.The licensing agreement will have guidance on having plans adjusted for local code, reviewed by architect/engineer etc. 

Manually accounting for the split paymentsYou can also get screwed pretty hard if they do something to lose their housing. 

Most HELOC"s ive found calculate interest on the average daily balance where the balance used to calculate interest was averaged over /30 or /31 days then multipled by rate/12 so this is not a true daily calculation.The other issue I've come up with is that we need a quick way to get the fudns to pay down the line and ACH transfers take 3-5 days sometimes so having an autosweep account that engages auto sweep daily really helps plus we dont have to do the manual transfer (micro manage your line pay downs).

we have a primary fixed loan plus an adjustable heloc.

I would not recommend BRRR until you have lived here a while and adjusted to life here and  made some connections while paying attention to what the market is doing, what is considered a good location and where the gaps are.

And then adjust for the growth in prices across time OR/AND adjust for price difference across distance if going a little further out than ideal.