Tips on cleaning out the inside of the frame rails on a Miata?

Hi guys. My journey with trying to preserve my Miata continues. So, I took off the front bumper and bumper bar in order to take a look inside the frame rails of my Miata since I tackled the outer portion already. I just came here for some tips on how to clean up inside those frame rails? I want to get as much dust and dirt out as I can, and if possible, the rust too. I then plan on coating it with Eastwood internal frame coating. Any tips on cleaning out the inside of the frame rails? Using water in the frame rails kind of gives me an uneasy feeling, so not sure what options are out there to clean it up. I have a quart of Ospho that I was thinking about how I could get that to work in there, but I have no idea.

I would just pressure wash it out as well as you can...Eastwood sells a paint wand of sorts made for spraying inside areas like that that is probably worth getting so you can re-paint it before closing it back up.

Power wash then compressed air to dry plus a few warm days and you should be Golden. 

Then blow out with compressed air and use something to work a rag in there to wipe up the dust. I attached my brushes to a drill and it worked great

Thanks guys! I was thinking if I wash out the inside with water, I could also use a heat gun to help dry it out? What do you guys say?

I would think that unless you have some way to make the heat gun travel through the frame rail, you'll be another victim of the notorious Inverse Square Law, where one end of the rail will be saying, "Dude! Careful where you point that thing!" and the other end will be saying, "What heat gun?"  Compressed air sounds more practical and more effective.

In reply to Stealthtercel :

Thanks! I thought that was a joke at first, but then I read it again and realized that you weren't kidding lol. I'll have to get my ear protection out because my harbor freight air compressor is freakin loud.