A quart is going to cost about 40% of a gallon, so if you're going to do more than 1 trailer or more than 1 coat, the gallon is the best deal.
PM, email or give me a call if you'd like formulas for Benjamin Moore in an extremely close Desert Tan, almost perfect 'Dark/aged 383' (like on the bows and racks I took), or Vietnam era OD. I didn't try for a mix for 383 to match the Gillespie.
You can get the bases in anything from flat acrylic to acrylic or alkyd semi gloss. You should be able to get it down there, and it's cheaper per gallon than HAZMAT for either Arvoe or Gillespie.
Steve