For painting a military trailer I would have the paint mixed locally at an auto paint shop rather than buying it online.
Another option is to find a chain body shop like Macco or One Day that markets "cheap" paint jobs and have them spray it. I've done a few military trailers this way (and so have several friends) and never paid more than a couple of hundred dollars for prep and paint. When you factor in masking, solvents, supplies, the cost of paint, etc. and the convenience of not having to do the job in your garage or driveway, the price really isn't much. Part of the logic is that it is almost impossible to make the sheetmetal perfect on a military trailer without over restoring it as they were never perfect to begin with.
The last time I did this (admittedly in 2007), I paid $250, which included $100 "off the books" after hours body work and prep (with the Macco manager's approval and at his suggestion), paid directly to an employee who needed extra money because he and his wife had a new baby. No muss or fuss for me and I got to spend "paint weekend" offroading.
How were the results? See for yourself (photos taken 3 years later):
That red looks awesome! Well done with that build! Only things getting done to mine are rims and tires to match the X and bedlinf the interior of the tub and also the whole frame then painting the outside to match the X. Or if that's too much bedlining the whole shebang.
Bantam civilian trailers came in two colors - red and green. There is no known exact match for the '46 colors so most who restore that era Bantam trailer use the Willys red or green from those years. I used Sebring Red, the color of my '83 AMC Jeep, which is very close to the old Willys Luzon Red.