Humidity sucks. Do it on a dry day.
There is a ton of info online about prep after blasting including everything from 'just get er coated quick' to steel temperature shall always be at least 3 degrees C higher than calculated dew point temperature....bla bla bla. One of the key things is this " """"If longer storage is planned, the parts should be primed with a non lacquer-based primer. A lacquer-based primer allows moisture to penetrate the metal’s surface, causing re-rusting"""....that comes from the same page that also says this, """" parts should be washed with metal prep — a dilute phosphoric acid solution available from auto parts stores....yada yada buda boom"""". It's all great info and there is always a 'good, better and best' way to do things so its probably 'good' enough if you hit it with the 'best' primer you can afford.
http://www.americandrystripping.com/protect-metal-abrasive-blasting/ We DID NOT do that last part.
I like the "just get er coated" attitude but check type of primer you're using and the lacquer. non-lacquer issue. After blasting and lots of blowing, we did wipe ....nearly everything.... down with a degreaser then used TAC clothes to pull the lint, dust and poplar fuzz off just before priming. If you're just doing your frame and not much on the body, just get er' coated.
Hambone is so right about the sand. Even after hitting every spot with an air nozzle, the pressure from the paint gun would find the odd pocket of sand which only adds texture. Years later I'd hit a bump on the road and sand would fall out of the window frames in the cab so it's a good thing to do limited blasting.
You're really going to enjoy working on a spotless truck.