I watched only a small part of Marshall's video. He went to great length to explain about the location of Hell. But I don't think he gave any kind of explanation as to where Heaven is. It would be far more difficult to explain where Heaven is on a round earth globe. Though he might use the "tent" definition which others have used, if he were ever to try to explain where Heaven is.
Yes, I think it is more difficult. Although, I have some ideas, especially now that I've had this whole FE thing on my mind during my Rosary. Given that Our Lord ascended, bodily, into heaven; and if heaven consists of whatever stars and planets we see within the Firmament, then it is clear that He ascended beyond that boundary between the earth and heaven. Job describes the Firmament as a solid mass: "Thou perhaps hast made the heavens with him, which are most strong, as if they were of molten brass." (37:18)
Yet, in a globular earth with an infinite expanse of the universe, one could be met with this image of Christ floating off into space, or the highest reaches of the atmosphere and simply teleporting to heaven (wherever that may be). Which, to me, disrupts the plain order of the heavens and the earth which God so clearly established in Genesis 1.
This globular view makes it difficult to determine if there is a "where" in which heaven is located without falling into some sort of modernistic reading of heaven as a "state of being" rather than a place. Knowing that the only heavenly "state of being" is that of the beatific vision of God. But, if hell is a place, then heaven must be too. And, if Our Lord and Our Lady have retained their bodies in heaven, there must be some sort of physical plane for them to inhabit. So, this leaves me to reason that the physical plane of heaven is located beyond the impassible barrier of the Firmament, as Isaias states: "Heaven is my throne, and the earth my footstool" (66:1) Which, in a way, makes God and heaven closer to us than the model of an infinite, lonely expanse of the universe.
And given the descriptions of Apocalypse chapter 21, it is apparent that it is a description of the physical abode of heaven wherein the glorified saints reside and move while remaining in this state of beatification. Precisely like how Our Lord acted on earth before and after His Resurrection, where He was in a state of perpetual adoration of God the Father while moving and acting in a physical plane of existence. I myself see a temptation to believe that when we die and are resurrected in glory, we become as statues who are immobile and contemplate God. But, I think the acts of the glorified Christ in the Gospels paint a different picture entirely.
But, really, this is all speculative. The FE model reasserts a direct order of creation as residing directly beneath heaven, and removes the unnecessary meandering through the endless vacuum of space by stating that heaven is directly above and outside of our created world.
Here's what the Catholic Encyclopedia states about the location of heaven:
Where is heaven, the dwelling of God and the blessed?
Some are of opinion that heaven is everywhere, as God is everywhere. According to this view the blessed can move about freely in every part of the universe, and still remain with God and see everywhere. Everywhere, too, they remain with Christ (in His sacred Humanity) and with the saints and the angels. For, according to the advocates of this opinion, the spatial distances of this world must no longer impede the mutual intercourse of blessed.
In general, however, theologians deem more appropriate that there should be a special and glorious abode, in which the blessed have their peculiar home and where they usually abide, even though they be free to go about in this world. For the surroundings in the midst of which the blessed have their dwelling must be in accordance with their happy state; and the internal union of charity which joins them in affection must find its outward expression in community of habitation. At the end of the world, the earth together with the celestial bodies will be gloriously transformed into a part of the dwelling-place of the blessed (Revelation 21). Hence there seems to be no sufficient reason for attributing a metaphorical sense to those numerous utterances of the Bible which suggest a definite dwelling-place of the blessed. Theologians, therefore, generally hold that the heaven of the blessed is a special place with definite limits. Naturally, this place is held to exist, not within the earth, but, in accordance with the expressions of Scripture, without and beyond its limits. All further details regarding its locality are quite uncertain. The Church has decided nothing on this subject.