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roller would be better thin the paint a little and you would get a good finish and not overspray.
to reduce weight remove ac, line doors with a thin sheet of aluminium. remove the metal mouldings around the doors on the outside.
upgrade to a vs brake booster, they are plastic.
Make sure you have the small vn brakes on the front a they are smaller and lighter.
all these would save weight.
Doesn't need primer..........ever read the label or only the front of the can All non-ferrous metals need to be primed with etch primer, so aluminium and its alloys.1) The best thing to get off the last of the residue, is acetone. Lots of acetone. I'm pretty sure a wire brush will just smudge it.
2) Prime it with a good outdoor rustproof primer. White Knight do a good primer for a decent price, and a 1L can should get you two coats all over.
KEEP IN MIND: If you use 2 litres of paint, that's 2 kilos of weight
I suggest you use acetone on the deadning, which leaves the factory rustproofing intact. Then fish oil the whole thing for rust protection, and once it's dried up, give it one or two coats of White Knight Rustkill Hammertone paint. That stuff does NOT need primer, so you save on paint weight