A few ideas for you:
A) The Nashbar frame route mentioned above, there are build threads here on the forums detailing how some folks have done this. I haven't done this, but Nashbar has sales all the time and their frames are already cheap to begin with, so they can be had very inexpensively (it's $100 right now). You could pick up a touring frame from them in your size and transfer a good portion of the components from the Jamis* for now and upgrade later when you decide you like touring.
If the Jamis is a little small for you, it might sour your experience.
* Perhaps everything except a more comfortable handlebar and likely the seatpost, the latter is probably a different size. The drivetrain and brakes are most likely compatible as are the wheels and controls.
B) Find an older (late 80's, very early 90's) MTB on Craigslist. These can often be had for about $100 and their geometry is very similar to modern touring bikes. I tour on an '88 GT Timberline and if you search the forums you will find others who have successfully gone this route as well. America is full of garages with mountain bikes that people have ridden only a handful of times and so have essentially zero wear on their components. Eventually they realize they are never going to ride them or decide they want a "more modern" mountain bike to hang in their garage and sell of their old MTB's on Craigslist.
C) There are other trailer options out there as well, in addition to the ones listed above, which are good options, I'll add one of the ones I covet - the Extrawheel trailer. This is in the same price range as that two wheel trailer listed above and has some advantages. Since you are already set up for light weight back packing, you don't need to go with the Ortlieb panniers displayed with it, there are a number of options for affixing a regular backpack.
http://www.biketrailershop.com/extra...Fad_QgodnisA6A
I'm not sure why you are so interested in the trailer though. Particularly since you say your ankles are troubling you and a poster above suggests that a trailer will exacerbate that compared to putting the weight on the bike. Trailers can be a little tricky to handle and have some not so obvious downsides as well. Say you want to take public transit? With a bike with racks you can put it on buses equipped with bike racks and some trains are set up for bikes. You can't really bring a trailer onto a bus, and it adds a whole 'nother level of difficulty shipping the trailer on a train. Maybe you are planning on doing every mile on your bike, and that's great, but sometimes it's nice to have the option, especially if you get injured, or are find yourself worn out or run out of time. Personally I like to use the public transit to slingshot me out of the urban area, so I can begin the cycling portion of my tour outside the city, instead of having to first traverse miles of suburbs. Just some things to consider.
If I were you I'd be tempted to mount a rear rack on the bike that can handle the weight of your pack and then attach a large, low sided basket to the rack to toss your pack into. It'll over hang the rack some to the rear, but if you are down to a 30 pound pack that shouldn't be a problem, especially since most of the weight will be over the rack/rear wheel anyway. Call this idea (D), add A or B and voila! You're ready to roll, since you already have the camping equipment. There are both commercial options for mounting a basket on a rear rack and DIY examples. I've seen some pretty clever and inexpensive solutions that don't look bad, and work just fine.
This basket on the rear rack is the kind of thing I'm talking about, but if you are just planning on using it to carry a backpack it could be much shorter in height and have the pack be held in place with bungees or other straps.
I've seen things like the loading tray from a domestic dishwasher re-purposed successfully in this role. They are a good height.
If you do go forward with the Jamis there are a variety of options for mounting more water bottles to a bike. Somewhere on the net there is a nice comprehensive list of these.
Please feel free to ask any questions of us, we like to live vicariously through each other, as we can each only have so many bikes and projects!