A downhole tool string component, having a tubular body with an outer diameter. A first, second, and third flange are disposed around the outer diameter of the tubular body at different axial locations. A first sleeve is disposed around the tubular body such that opposite ends of the first sleeve fit around at least a portion of the first and second flanges, forming a first sealed pocket around the outer diameter of the tubular body. A second sleeve is disposed around the tubular body such that opposite ends of the second sleeve fit around at least a portion of the second and third flanges, forming a second sealed pocket around the outer diameter of the tubular body.