If the interior is visible from ouside (which if your doors will open on shore, it will be), you need to make it a part of the main model (the 3p mesh), though in pretty low detail, because it will be seen nly from outside.
Then you make a separate model, with most of the outside mesh removed (if it cant be seen from outside), and all the tris you saved by this then can be put into the inside model, to increase its beauty
For this particular vehicle i would suggest making one 1st person model for the driver and whoever else will be on ther deck (1p LOD0), and one for the guys that will be in the troop compartment (1p LOD1).