Fantastic boilers and back up service when problems occur.
Look at it like this how much do SpaceX & NASA spend on rockets and how many problems do they have, just because something costs more doesn’t mean it’s going to be fault free.
I’ve had to do this once, I wasn’t happy about having to do it, but that’s what the customer wanted, so that’s what he got. Must of been in for about 7 years now and not heard anything from him.
I screw to the floorboards or chipboard either backer boards or 9 or 12mm ply depending on the floor and position on the joists, then flexible floor tile adhesive to stick the tray down