What i did...
1. I attached the tray to the spacer first...(don't forget your straps....) w/ small screws(4) and countersink them so as to not hit on the battery itself.
(I also have a thin piece of foam on the bottom of the batt tray as insurance)
2. Line up tray and drill 4 small holes thru chassis. Install screws thru chassis and into spacer careful not to screw into tray itself. Don't forget to counter sink screws that go thru chassis.
This is not hard just a pain the in *** Be careful on the size holes you drill into the plastic. Remember, you need enough meet in the plastic to thread the screws into.
Good luck!
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3. MBX-5 ONROAD CONVERSION 1515, MMM ON 5S
4. MRX-3 ON ROAD CONVERSION 1512, MMM ON 6S
5. TEN T 2650 T8, MMP ON 3S