I've painted 5 jets using 3M masks and Iso's, and have had no health issues (knock on wood). These jets were painted in my driveway with little to no breeze, wearing goggles and skin fully covered. As Terry stated, I store my mask in a ziplok but I replace the cartrigides 2 weeks after opening regardless of use.
I purchased a forced air respirator earlier this year and I use it when forced to paint in the garage due to weather. This is the safest way to go when using these types of paints.
I asked my paint guy about 3M masks with Iso's and he said I was ok if outside and not enclosed whatsoever.
In regards to a paint gun, I have a Sata minijet4 that I use strictly for clear coat. Outstanding gun but it's limitation is cup size. The cup that comes with it needs to be twice the size.
For primer and base coat, I use a CAT minijet/detail gun. This gun used to sell for $100.00 on sale and includes 3 tips/nozzles and a bigger cup is available. Sprays like the Sata, smaller fan size though, at half the price.