Are you discussing the addition of a horizontal sliding hatch to the deckhouse top you posted construction photos of, or are you talking about a vertical access into the house?
Either or both ways, I like the garage idea.
On my boat, I have a sliding hatch atop without a garage that has a big sweep seal along the front that is sandwiched by rail guides, and two removable vertical panels that make up an inverted triangle that drop in to close up the cabin -a pretty standard design.
I don’t have enough room in the cockpit to split the “doors” vertically and hang them on hinges to have them swing open, and I don’t care for having to store the X2 panels somewhere in the cabin (especially since I added a fixed window to the upper section) or the inability to quickly close the cabin.
And so I have come up with a design where the horizontal sliding hatch atop and the X2 vertical panels are all hinged together so that the cabin access panels swing and fold over each other, and the stack then flips over and lays flat atop the back half of the top sliding hatch, and the hatch then slides forward along the track to provide extra headroom and airflow in the cockpit.
The vertical side guide rails for the X2 vertical panels that used to catch the drop in sections are then hinged instead of fixed to allow them to swing out of the way so the sections can articulate, but then provide good security and sealing of the panels when closed and locked.
My reason for mentioning this is to point out there may be an opportunity to do something similar since you are building from scratch where both the vertical access doors and horizontal hatch are one system that folds, slides, and stows into a garage for protection while creating minimal intrusion into cockpit or cabin when being opened or closed.
If I’ve misunderstood, or being that it is a big boat you have plenty of room for a traditional hinged door type access, never mind.
