@Costin I.
For myself, I wouldn't bother setting up a trust or escrow account. Its just funds sitting with my "reserves/savings" --- whatever you want to call it.
If you manage your money by account, then by all means create another savings account, or whatever account you use. (personally, I use a brokerage account so I can get the pretty risk-free 5.25% in a money market fund that is completely liquid).
To be blunt, if you really are limited in funds... Then, the first tier of funds to have on hand is for repairs and smaller repair/replacments. For example, a leaky faucet or toilet. Nowadays a plumber costs a bit, but you need to have "$100's" handy. Every 7-10yr'ish you need to replace a water, or whenever it goes, so maybe $1500. Since you have three properties, if you can afford to have ~$5k handy in case all three go at once that would be nice. But what are the chances --- until it happens LOL
Of course, you need to save up potentially for some vacancies... Hopefully, you don't have all three go vacant at once.
Then, you need to have a plan for larger expenses such as a new roof, driveway, etc. Granted, if your plan is to swap properties before major capital expenses, that makes it easier --- pretty standard plan.
Otherwise, just use whatever investment plan you have for the extra cash flow. You need something to complement real estate since its usually done in large chunks of money.
Good luck.