Probably telling you all how to do something you know;
I found the best way to clean the chassis tubes on both the TrakKart and the Barlotti, was to use a wire brush attachment on the angle grinder, and just spend 1-2 hours taking all the paint, and surface rust off the chassis tubes, at once, the use a tin of (aerosol) acid etch primer to protect it before painting.
This seems cheaper than shot-blasting, and it's quicker too (no need to ship the chassis off to the blasters)
This worked really well for the TrakKart, and Barlotti; although the last step might not be so applicable if powder coating.
-Steake