Okay, I'll see what I can tell you about firing at LVTs...
First, when trying to hit them with ordnance in the lagoon, they are +2 for moving/motion (almost always), and an additional +2 for wading. Fortunately for you (sounds like you are playing the Japanese), there is also the -1 for large target size. So before acquisition, you start out at +3. So that is a good reason to buy the 37Ls with a ROF of 3.
Your 50mm mortars, of which you have zillions, are also good for shooting at LVTs. The water will muffle the explosion for half FP, but the low armor and being OT will mean your 1FP attack has a real chance of doing something. It might seem like a low odds attack, but add in some 10 or 15 of them, and the dice have to give you something good sometime. These mortars are more effective when you can hit the LVT while it is sitting on the hard sand beach.
Assuming you get a direct fire hit from that 37L on an LVT in the water, there is a +1 to the TK DR for a hull hit. More cushioning from the water. This does lower the chance of a burning wreck, which is not bad. As a Japanese player, I'd rather see survivors trying to wade in than the plume of smoke for follow-on waves to hide behind.
As for Carriers in D6.8, they were not at Betio. Vehicles which are Carriers are listed in the British vehicle notes.
As for CE passengers, we're trying to clarify their ability to firegroup their inherent FP with the MG armament of the LVT with Perry. Otherwise, if they stick their heads up, hit 'em with the 0.50cal HMGs. You did buy 0.50cal HMGs, right???
Just the tip of the iceberg of BRT--have fun! If you have other questions that come up during your game, send them here. Some good Betio veterans are around...