Hey! I'm getting into a 2020 144 soon and it's more than likely going to come with the auxiliary battery under the seat so this has been super helpful! Do you happen to have any more pictures/measurements for that wood/metal tray you made? Hoping to do the same thing with the heater and battery under the seat.Mostly the mounting bracket for the heater. It works well and has good airflow. But it turned out to be overly complex. I thought I needed it but after I built a the battery bracket I think there is enough room to just mount the heater on the floor.
Basically it’s over engineered. In the end though I did only drill 3 holes, and their positions were a little less sensitive to errors. So there were fewer opportunities to really screw up.
Nick in VT