Enough old timey talk. Displacement tons were introduced originally to create a method of mapping deckplans. This led to many many ships with rectilinear corridors, rooms and darned near everything else. It works. It's simple and as always I'm not leaving it alone.
So here we have the classic 1.5 meter squares representing staterooms and corridors. I made a few adjustments in keeping with common deck planning conventions. Each grid represents one stateroom or enough area for two people to live in without killing each other (barely). Now many people designate 3 dTons for each stateroom and contribute the other dTon to communal facilities, whatever your culture/species needs: mess, meditation area, showers or flat rocks and sunlamps.
I represented this fraction with the neon blue. So in other words the white area will hold 10 people not 8 but remember that some are sleeping and some are in the communal area.
The pink is an extra 20% of area that is supposed to go for corridors (pink in the example). You can see that's not a lot to connect five compartments with flair for decorating.
On the right I have, the hexagon. It's pedigree in RPGs is nearly as old as that of the square. Back in the day Avalon Hill had a trailer truck delivering pallets full of hexagons to crank out wargames. Sadly the hexagon never found its way into interior mapping (unless you're playing GURPS).
The pie slices of the hexagon are 3.73 meters in length by 4.84 meters maxand take up 13.55 square meters. A 1.5 meter square is 2.55 square meters. The pie slice takes up 6.02 squares or 3 dTons. The corridors are 1 meter (okay I cheated) by 4.8 meters or very nearly 3 1.5 meter squares if you must grid things. yes the area of the little joint sections was figured in. Use SketchUp or Wings and check on me if you doubt. I halved the amount of corridor area for figuring dTons because you're sharing it between hexagons or the outer hull's armor, insulation and greebles (greebles take up no tonnage. It's a fact.)
Moreover the twenty percent for corridors is already laid out. You can get to any compartment in this hexagon and your area for corridors is prefigured. The center hex can be a fresher or DC cabinet etc. You could make each hexagon contained with very cramped facilities for showering, cooking, laundering and sunning yourself on a rock (one at a time please. Or you could specialize the hexagons, one had a mess and galley, another showers, another a utility room.
Each hexagon I laid out comes to 20 dTons, giving you an easy way to lay out a ship of 100, 200, 300 etc tons.
Hexagons are very sound structural element to build your ship around.
The corridors do a lot of bending when you have more than a couple but this has benefits. Neither bullets nor radiation can turn corners. This is handy in a resisting a boarding action or when there's a radiation leak.
I'm still fiddling with the hexagons. Obviously you can also split a hexagon in half or thirds easily enough to make odd shapes ot give yourself a straight length of corridor where you want it without straying too far from the sacrosanct 20% corridor bonus.
The benefits of using the hexagons for a tail lander should be obvious: the dang things stack like poker chips. They can also be used to lay out the ubiquitous domed colony. A center hex and six surrounding hexes makes a rough circle.
As a final note, if your characters are used to a square grid sic some aliens based on bees after them and use hexagons (or triangles or even gasp! circles!) for their construction. that will remind your characters every moment they are in a structure not built by man.