The lower tray makes it kind of tough to see the throttle servo and the receiver. That's why mine is removable. The kit provides a hardwood block to cut and glue to the fuse sides as an upper tray securement point. I elected to use home made aluminum tabs with nuts and bolts, but the hardwood will be fine using simple 2-56 sheet metal screws if you want to. A total of 4 screws would be enough. That would be faster than my method, but a little heavier.

Should you elect to install a tray at the location I noted, it would be well worth taking the time to survey things to see how you can work with plugs and such before you nail down the covering again. On mine I can access the battery plugs, but not the switches or batteries themselves. Before you decide where to place the batteries, try to complete as much of the assembly as you can to obtain a rough balance at 6-3/4" by moving the batteries and rudder servo prior to attaching them. Should you need to, a single rudder servo in the tail works just fine if you add a little additional support around the rudder horn point.

The plane WILL balance without any extra weight with engines from 50 to 62cc, but parts placement becomes critical with larger than 52cc engines. If you're using a DA50, the batteries will likely need to be more forward than mine are. BTW, the batteries in mine are Fromeco 4,800 and 2,400 Lithion Ion for reference purposes. Lighter than nimh and nicads.