Cake supports

Your plastic rods are OK.  

You need to cut them with a mitrebox (miter box) to make sure the ends are all square and that they are all the same length per tier.  Make sure there are no sharp nubs along the ends (you can use sand paper and then wash them).

I use bubble tea straws for supports and cut them with a scissors--strong, simple, cheap. 

For a very tall cake like that, I'd also put in 2 full length wooden dowels (cut with branch pruner, sharpened in a dedicated pencil sharpener, wiped down with grain alcohol, greased with crisco, and gently hammered in) if it's going to travel stacked.

I place all of my cakes on 2 layers of memory foam in the back of my van, too.  Road vibration can kill a cake quicker than a hungry toddler.

HTH

Rae

the sps is the way to go. I did a five tiered cake this summer. not only was it tall and heavy, it had to be moved from a display room to the main room for cutting.  it made putting the cake together an cinch and there were no problems at all in moving it from one room to another. even better, the catering team thought it was the easiest cake to cut that they'd ever done. 

here's a long CC thread which describes it all

http://cakecentral.com/t/603925/sps-instructions

SPS is Single Plate Seperator

I use bubble tea straws for all my cakes (including the 5 tier cake in my pictures).  I then hammer (literally) 2 wooden dowels with a sharpened end through the entire cake.  I offset the wooden dowels from the center.  This way the tiers can't "spin" like they could with 1 center dowel.

For SPS info, read my signature line.  Once you use it, you'll never cut a dowel again.