I will strongly vouch for permethrin on clothing. It is incredibly effective against chiggers, ticks and mosquitos alike. Both my wife and I (mostly her) did a lot of field work at Ft. Bragg during our Ph.D.s, where the chiggers are absolutely SAVAGE. Clothes treated with permethrin always kept them away, whereas one day in the field without always led to an itchy and painful week with dozens to hundreds of bites. I still have socks labeled with "P" to indicate my field socks. xcellent tick and mosquito control is a bonus, but those critters really pale in comparison to the exquisite torture of chiggers. When applying, be sure to focus on socks, underwear, waistbands, and anywhere that generally gets hot and sweaty and is close to your skin. It will get expensive (and result in unnecessary exposure) to treat all your clothes so I'd pick a few field outfits. The permethrin will last six or seven washes. If you are cheap and daring, you can buy agricultural grade permethrin, but we always stuck to the stuff approved for use on clothing... There has to be a reason for the large price difference.
Between all of the chiggers and the lush, green fields of poison ivy, I really have a lot of sympathy for anybody who has to train at Ft. Bragg.