Second option – a new mic, as you seem to be thinking. You’ll want to go Dynamic in a noisy room. I recommend, above, the Rode Procaster as a great mixer-compatible dynamic mic. The Rode Podcaster is cheaper, but USB only, so wont work with the mixer, but you could actually link that up to your iRig setup, I think. It would be interesting to hear how that would work in your truck in terms of cutting out some of the background. Not sure how you’d rig up a stand, but could be a project! Finally, the ATR2100 (or samson Q2U for outside the US) is a great little dynamic mic too, so that could be a much cheaper option to cut down the background noise. The benefit you have there, too, is that it’s both USB AND XLR, so could be used both with your mixer, and portably.