I totally get the wanting lower gearing, and amongst my bikes is a touring bike that has a mtb crank like you are thinking of, and they work great for loaded touring in mountains....
BUT
you are going to have to start adding up the costs, including labour, and you might find that it adds up---now I dont know your Raleigh, but do take into consideration that if its not made for touring, you'll still have a frame that may not have the ability to take a front rack and panniers, short chainstays, and generally a frame not made/ideal for carrying more luggage if you get into that
I wonder that after looking at a realistic assessment of the final costs involved, it might be more effective to look for a good used touring bike that will have all the advantages of a touring bike designed for carrying panniers
I think the 2015 clubman should make a good touring bike. I already have all the racks on it (I have done a couple of small tours and use it for commuting about 30km each way to work in nice weather). It was described as light touring on their website (and I now beleive this is because of the gearing). It has long chainstays, etc. The frame actually looks a lot like a long haul trucker except the top tube has a bit of slope to it (and it was much cheaper). I would post a link to a photo but I don't have over 10 posts yet.
In terms of cost I'm not too concerned with it (although I'm not being silly about it). I'll be doing all the work myself because I enjoy doing that sort of thing and also because I think it will be good preparation for fixing issues out on the road when that happens. I have added up all of the costs of parts and that combined with my bikes original cost will still be far less than buying a surly or salsa touring bike (plus I've already gotten 5 years of good use out of the bike). The other thing about these factory touring bikes is that they often don't have the gearing quite as low as I would like it so I might have to make a few modifications to these bikes as well.