I have 2 Predator 3500 and 2 ryobi 2200. You can connect any of them in parallel in any configuration. Even more than 2. I can run a 50 amp coach, no problem. I can even hot swap to refuel.
The predators have the extended warranty from HF, so when my first pair got to 1 year 11 month I just walked in with the two of them and they gave me two brand new ones, no questions asked. I bought the extended warranty again.
Just to be clear, although it sounds shady, THIS IS WHAT THE STORE MANAGERS FROM TWO HF STORES TOLD ME TO DO.
When I went to exchange them, I just strolled in with the two of them and the cashier asked me "Two new ones, right?"
Doesn't get much better than that...