I use Paulson or ASM/CPC chip boxes for shipping high-end clays, but i think you will be better off using USPS large padded bubble envelopes for those RTPlastics chips, since plastics won't chip or cause wear marks during transit.
Hold a padded envelope and load up a long barrel (~65 chips) along the bottom, roll it up tightly one or two rotations, then add another long barrel, and roll it tightly up too and seal. You'll get about 130 chips in each envelope log, then put 3 logs into another padded envelope and seal.
Put your two final envelopes (~780 chips total) in a Priority Medium Flat Rate Box with lots of tightly-stuffed padding around them, to the point where nothing moves whatsoever. If you shake the box hard and hear or feel ANY movement within, it's not packed tight enough. Use styrofoam peanuts, bubble wrap, crumpled brown shipping paper or newspaper, or more wadded-up padded envelopes to totally surround your inner package.
Tape up the box with shipping tape, covering the entire box in both directions, including all corners and seams. Put clear tape over the shipping label too, to protect it from tears and water damage that could cause it to become unreadable. For very valuable chips, i double-box (a MFRB within another MFRB), and add cardboard reinforcements to the inside box corners.
USPS padded bubble envelopes are free, and work great for many shipping applications. If your local post office doesn't carry them (most don't), order 100 online (10 packs of ten each). Free shipping, too.