I have 2 of those units and a parallel kit. They're great!
The 53 db is at 1/4th load. Which it will stay under charging batteries. But it does kick up and get a bit noisy once you start running electric appliance. Not near as bad as an open-frame generator, but you won't make friends with camp neighbors if you run it under full load often.
Normally for my trailer, I only bring one unit, and it's mounted in an XL plastic tote, with an attic van in the lid, some holes drilled in the bottom for intake, and some heat shielding and steel-wool (for further sound absorption) on the exhaust side of the tote. From 25' away its imperceivable doing it's battery-charge duties. You only hear it when the microwave or electric kettle is running. I only run it from propane when it's closed up in the sound-box, because it does run noticeably cooler on propane.
I run the parallel kit when I have the van setup for special events. Not just because of total load, but because the audio system, irrigation pumps, and lights all have high peak-loads. But not at the same time. I've never tripped a break running the parallel kit, but had issues with my previous generator tripping easily from peak loads, even though the overall load on each unit is about the same. (you can see the generators at the back of the dance floor at about the 3-min mark here
https://youtu.be/HJYeK_i5krs )