Not that you asked for them but here is what I would look at to mount the ECU and battery.
1) battery. I would try to mount it somewhere on the front of the motor. Grab a couple bolts from the accessories and build a little tray for it to sit on. The reason why is weight and visibility. battery cables are heavy
. so even mounted in the belly you are running big cables up to the starter and winch. Mounted on the front of the motor in your case (because you have no lower chassis structure) you will have super short battery cables. They will weigh less and work better being short. It will also not be in you line of sight AT ALL. An aluminum box on top the trans blocks your view of the passenger front tire from the picture you posted.
2) ECU. I'd mount it to the rear of the motor with the plug facing down. Easy enough to put rubber mounts and wrap it with heat shielding. I see plenty of OEM ECU's mounted to the fender on the hood.