I agree that Romans 7 should not be isolated, but, I have a different take on Romans 8. I don't think Romans 8:1-17 is necessarily teaching us how to mortify sin. I think it is teaching us how God will mortify sin within us, as we keep our focus correctly on Christ and his promise to follow through with what he began in us. A lot has to do with how you take the phrases "live according to the flesh" vs. "live according to the Spirit", and "walk according to the flesh" and "walk according to the Spirit." My explanation here is quick, as it is late, and is therefore probably not detailed enough to be plainly laid out so that it is easily seen.
I think he's speaking in Ch.8 vs.2 about freedom from the condemnation of the law. And, righteousness (imputed) in vs.4 comes by resting and abiding in the finished work of Christ, instead of resorting back to works of the flesh and hoping in it to produce our righteousness. Vs.5-11 compares those who think they live (have eternal life) by fleshly means verses those who think they live (have eternal life) by faith in the work of Christ; and shows what each resort to for their sanctification. Vs.11 says that life or redemption of your your mortal bodies will occur, and that the Spirit gradually gives us life now through his sanctification work within us. Therefore, vs.12-17 shows that the accusation laid against Paul in Ch.6:1 is a false accusation, for grace does not lead to liscentiousness. Rather, it leads to life or sanctification being given to your mortal bodies in this life. Vs.13 shows that sanctification comes by the Spirit alone, and all reliance upon our deeds of the body towards such are to be abandoned. We are not to fear that we will be condemned for our remaining sin, vs.15. We have been adopted, we are his sons, we are heirs with Christ, and we must suffer through the likes described in Ch.7, so that we will be glorified with victory in the future when Christ is glorified.
Paul considers in vs.18 that these sufferings with sin aren't worthy to be compared with the future glory of victory he'll receive later. All of creation waits its redemption from bondage to sin just like we do (vs.19-22). Our deliverance from sin lies in hope, and in this hope we were saved from the laws penalty (vs.23-24). And, we wait for our deliverance from sin with patience (vs.25). In the meantime, vs.26-27, the Spirit helps us with prayers to Christ on our behalf. God is in control of everything, and is causing even our struggles with sin to work together for our good and for his glory (vs.28). We are guaranteed to be glorified, and freed from our sin, since we have already been justified (vs.29-30). There is no break in that link. Vs.31-39 assures us that God will follow through with our sanctification and glorification. Both are guaranteed to us. No charge can be brought against us for our present sin within us. No condemnation, no separation, nothing we face is able to rob us of the promised glorification.
So, I don't think he's switching from discussing our indwelling sin and it's power in our lives in Ch. 7 to a strategy for how we can mortify our sin within us in Ch.8. I think Ch.8 rather continues the same theme as Ch.7, and gives us hope in the midst of a Ch.7 life, while pointing out that the accusation against Paul in Ch.6:1 that started this entire 3 chapter discussion (6,7,8) is a false accusation, for resting and abiding in the finished work of Christ leads to him sanctifying us now, instead of resorting to looking within ourselves and striving with deeds of the flesh. If the Spirit is what made us live in the first place, then we must daily keep the same mindset for our sanctification. That's what he means by "walking by the Spirit". We are to stay rested upon God and relying upon his promise to sanctify us.
So, the Psalm 130 fits well, and vs.5-8 show that we are to wait for God in hope for deliverance from our iniquities.
That's how I see it for now.
Blessings!