With a few of our STRs being glamping tents and RV sites, the cost of a policy to cover a the repair/replacement of a tent or picnic table is not worth it in my opinion.

And I know cashflow isn't everything in the beginning an can come with time, but I don't want to acquire a bunch of properties where I'm only going to net 100 / mo after PITI, because with those margins all it takes is one repair to wipe everything. 

Hypothetically if I win a bid, then would I be able to utilize a HML for any possible repairs now that they'd have access to inside the property?

To build that kind of portfolio you will also need help with financing, locating, inspecting, repairing, etc.

But how can we draw a line between repairs and replacement?

It is almost as hard to buy a fixer upper at a price that will cash flow after repairs. 

If the property is bleeding money every year from repairs, maintenance, or turn over you'll never get ahead.You can tap equity with a HELOC (challenging right now), cash-out refinance into a new loan (much higher rates), 1031 exchange, or sell (tax hit) but the numbers and property condition need to guide this decision.

I got free repair estimates (inspections) from two roofing companies.  

Roof was flashed and repaired in May.

Is this a low number for both vacancy and repairs?