I use .5-.75" MDF, zip ties and/or hot glue.
Drill holes though the MDF for the zip ties then use a router on the bottom to cut a .25" line between each set of holes so the board can sit flat. Or if you are mounting the crossovers externally, you can built a box out of red oak or another nice wood.
As for chassis wire, what are you using for speaker wire?
I normally use Neotech solid core, but may try Duelund next time. When using solid core, remember to twist or braid them.