I have a Downtube VIIIH and will have a DT Mini any day now.
I'm going to use these bikes as part of my big adventure that starts next year when I retire and set off on my sail boat to points south (Mexico & Central America) and beyond (South Pacific). As with all things when traveling to remote parts of the world, a proper tool and spares kit is required.
I have pretty much every normal tool (allen wrenches, regular wrenches, sockets, screw drivers, etc) in both standard and metric sizes that I might need but I'd like to have recommendations from the experts on this most excellent forum on what I should have for bike specific tools and which brand / style you believe will hold up best in a marine environment. So, for example, what tire levers do you recommend (material, manufacturer, quantity) as well as any other bike peculiar tools?
On the spares, obviously I should have spare tires and tubes but what else do you think will very likely fail? Please feel free to recommend brands that you have had good luck with.
The bikes will likely get weekly around town / village use in most places and some serious day trips into the country side in others.
Finally, other than the saddle, grips and tires, is there anything that you would recommend be upgraded from a durability / maintainability stand point? I'm a little concerned about the looks of the shift and brake cables.
Honestly, I believe you made very wise decisions going with DTubes on your journey. Pretty much anywhere you go in central america you can get help for the non-proprietary items (the entire bike!). I would take some spare spokes for both wheel sizes and make sure, before you go, the bike is properly lubed (something that DTubes do not come from the warehouse ready to face oceanic corrosion).
Good luck on yuor trip, make sure you share some pictures with us!
I'd check in the Touring forum for optimal advice. But....
Since you're traveling by boat, I'd bring more stuff rather than less. Lots of spare tubes, a few spare tires, I'd also get extra spokes, extra chain, lubricant and maybe even an extra derailleur. But really, given the nature of the trip, if one or both bikes gets stolen or utterly destroyed you can always get another bike.
If you're worried about the brakes, it looks like the VIII or whatever can be equipped with disc brakes, could be very handy for the rougher roads down there.
I wouldn't worry too much about the tools. A typical multitool will be fine, just get one with a chain tool. Keep it in a ziploc if you're worried about it getting wet.
Also I suggest you email Downtube and find out in advance if they can ship any proprietary parts (e.g. handlepost), or even a full bike, in some of those locations.
Since you mentioned tire levers, I own a Crank Brothers Speedlever and I really like it. http://www.crankbrothers.com/speedlever.php
For the really though to mount and dismount tires I use one additional generic plastic tire lever. Both are made from some type of plastic and won't be harmed by salt water.
If you stick with larger volume, lower pressure tires, you should not have any problems finding replacement tubes and tires at least for the 20" wheels.
I would definitely not switch to disc brakes. Disc brakes may not have made it to some of the places you are going to visit, yet. Whereas regular brake pads (even if they are not name brands) will most likely be available everywhere.
Since the bikes will be at least somewhat exposed to salt water, I would frequently lube everything on the bike with a "heavy" waterproof lube. It might be a good idea to fill whatever empty space there is in the cable housings with grease.