Mounting battery in trunk

[Ray Sta.Juana]

I just got the cable routed through to the trunk and now I'm trying to
figure out how to fasten the battery box to the floor of the trunk. I'm
using a Summit metal battery box(non sealed) and I need some ideas on what's
the best way to bolt it down. Here's the link to the box:

http://store.summitracing.com/partdetail.asp?part=SUM%2DE890101

The thing I'm wondering is the trunk is far from flat and the bolts holding
the box together are not flush with the bottom of the box. Should I use
spacers or a piece of wood to even it out then bolt it through to the other
side of the floor? I looked through the SE-R archives but didn't find
anybody who've used this box before, mostly the sealed kind. TIA

Ray S
98 Sentra SE w/ mods