Depending on how much mud you are going to run in the next couple of years, Baja MTZ give you good street milage compared to MTR's which is a very good tire also. KM 2"s are a good choice also haven't hurt any complaints from folks I wheeled with them. 35's should be ok provided you don't go crazy with them.
I was between the MTR's and the KM2's, but I have heard so many good comments about the KM2's, that I kind of went in that direction... As for mileage, since this will become the wekkend toy, I dont really care that much. Noise is more of a worry, as some trails are a couple of hours by highway, so I dont want the Jeep to sound like a WWII bomber... But SOME noise is OK.
35's should be ok provided you don't go crazy with them. If you are going to wheel a lot upgrade the front shafts with the 35's the stock ones will spread the yokes fairly quickly
I already upgraded both axles to SUper 35 and SUper 30... G2 alloy shafts on both ends with the bigger U-Joints up front. What worries me about the 35's is (1) wheel speed for cleaning the mud out and (2) spare tire (I dont have a carrier, and I know the 33" can ride on the stock carrier, but I am not sure the 35 will fit). But since the investment in tires is similar regardless of which size, I wonder if it is worth it to go to 35"...
I'd check into the Interco TrXus MT. I had a set on my 01 and couldn't have been happier. They were cheaper than BFGs by a good bit and did well on ALL types of terrain.
Are they radials? The Jeep will be sitting at home for long periods, so I am not sure how a bias tire will handle that... Cold is not a problem, as the record low in Panama is probably well above 60*.
What tires are prevalent down there? I'd also go with a size of tire and brand that's readily available as well. How much street and now much dirt? Most of the tires I've seen have been BFG's or Interco SS's down south. I'd consider using what works there rather then here. Although there are places in the US with similar red-clay. Red-clay is really sticky stuff unless it's really wet in which case it turns really slimy. Sticks to everything too. It will stain anything and everything red over time. Not to mention rust as well. For that sort of stuff, I'd go Swampers. You won't really have to worry about it getting too cold and I'm sure they are readily available there as the LTB's are specifically made for the SA market.
I'd think about doing an axle swap though. I'm sure it will be easier to gather parts while you're still in the US then in Panama.
I thought about the swampers, but the noise worries me a bit. When I used my cousin's FJ Cruiser, he had 36" Super Swampers, and it was noisy as hell. On the other hand, many people are running BFG and they all say they work well down there; I know that the KM's work perfectly, but not that many people are running KM2's yet... We do slap on some chains when it gets really bad, though.
