Hey!
Well this no K car but this will give you a good idea on how to mount your RCM battery tray and what you can do to make it fit without using spacers.
http://www.rc-monster.com/forum/show...ght=808&page=4
You can mill the bottom of the tray so that the nuts or the sideguard wil fit inside the tray if you know what I mean. Anyway just check the bottom of that link, pics are worth a 1000 words :)
Hope it helps