A tube is really just an air bladder. If the tubes you have are working fine and don't have any patches or other noticeable flaws, I'd just re-use them. But that's me.

I've run Marathon Plus's and I recommend them for being a bulletproof tire. But I personally prefer Panaracer T-serv (for messenger) tires for touring. They last a long time, get very few flats and weigh less than half what a Marathon Plus does.