Difficult to answer without knowing what sort of supplies that you have handy. My first "spray booth" was nothing more than a cardboard box, about two foot square and a foot and half tall, open on the front and top. For your situation, you probably need something more enclosed. Dimensions are not overly critical, as long as it is big enough to allow you to comforably paint whatever you are working on.
Maybe a tarp, preferably clear for better lighting, could be tented over a large cardboard box, pehaps attached to the side of a vehicle. Alternatively, do have some sort of tent that could be used as is? One major concern if you enlcose yourself with you model would be ventilation. You want to be careful that you don't gas yourself.
Even without full enclosure, I would think that a large box, open only on the front would help a great deal, and then cover the front with a tarp while the paint dries.
Good luck.
Andy
P.S. Thank you for your service over there.
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