Activity Time and tanks that are meant to hold long sight lines

Several nations have tanks that are best-used holding long sight lines (Germany, Sweden, Some US tanks, etc.). In those vehicles, it's often hard in lower BR brackets to maintain a high-enough "activity time" to complete certain rewards/challenges that call for the usage of those very vehicles (Hull-down-amenable TD's, etc.). I usually resort to just rushing in those vehicles to complete the challenge. What do you guys end up doing, if you are forced to play those vehicles? Just, don't and miss-out on the challenge? Pay to change it? Use a nation that doesn't hinder you from rushing?