Sorry to hear about your loss and I understand how valuable some of these items can be to a family. I do have several questions that would need to be answered so I can give you the best advice possible.
Are we talking about a toy metal truck? Or is it a full sized tanker?
Do you have paint equipment like a gun and compressor or assuming it's a toy truck, where you planning on using rattle can paint?
Is there rust still in the pits? Or where they not that deep and where you able to sand the rust out?
Pictures would help.
Just need a bit more information to give you the best advice.