Here the Holy Spirit is the Baptizer and here it is the "immersion" of the believer into the Body of Christ. Both baptisms are spiritual and simultaneous upon conversion. Thus the believer is "in Christ" and remains "in Christ", and also has the indwelling Holy Spirit.
Until you have experienced the second move of the Spirit in your life, you will continue to deny the existence thereof. when we are Born again we receive an "earnest" of the Spirit, which is literally a down payment, then later in our walk we receive a fulness of the Spirit. When Jesus Speaks of the virgins and the Oil in Matthew 25:1-13 this is what he is speaking of (Having enough oil).
I grew up in fundamentalism, and they do not teach this, to their own detriment. When I was young I had the Baptism of the Spirit in my Baptist church, I tried to express this to the adults in my church and was told to not say anything. They were afraid of this. Therein IMO lies the problem in modern fundamentalism, a spirit of fear rather than the fulness of the Spirit.
I encourage you as a fundamentalist to let go of this spirit of fear and move onto the fulness of the Holy Spirit.