you just need a property manager, they don't specialize in MTR, they are the same as those that manage other types of rentals. 

My strategy is to invest in rental properties for cash flow and consider flipping opportunities when appropriate.As a beginner, I'm seeking guidance from experienced investors who can help me navigate the landscape and avoid common mistakes.

Read BP books (The Book on Rental Property Investing, Managing Rental Properties, Set For Life), watch Youtube videos, etc. 

I plan to one day aquire apartment buildings for rental income.

It’s often sold as an alternative to larger security deposits or co-signers for people with bad credit bad rental history.

OR if you want rentals simply connect with those that provide them, LI is NOT the place to do it, too expensive and little to know return, you're lucky if you get 4% net .

My follow-on question is how to conduct market research on demand for motorhome/RV/camper rentals.

Perhaps with only one rental in the portfolio, we were a fish too small to bother with. 

We have two rentals in Ohio, one SFH in Richmond Hill,GA and one multi in Savannah, GA.

Yes there are a lot of HELOC options for rental properties.