It's is alot of work, but when you are done, you are gonna love it. I don't now how to make a direct link, but if you do a search for "Extreme Expedition Vehicle here on SS, you will see some pics of our M35A2 we did (that's Army Bob on my avatar)
The best thing I can say is built it using YOUR skills. We run a metal fab shop so it's natural to use steel all over. If you're better at carpentry, then get sawing! Find a good used camper or trailer and canibilize it for parts. We used windows, stove, sink and misc other parts from a cabover camper given to us.
However, don't skimp on your electrical or electronic parts and pieces. We went through two cheapo inverters until we spent the $$$ for a good one. No problem now. Same thing if you go for propane - don't cut corners!
Is your M109 in good reliable running condition? Don't go to all this work and then have the silly thing strand you at the top of a mountain. Make sure the truck itself is 100%. Army Bob was and still is in awesome running shape and we trust it completely.
Also, be prepared when you take it out, lots and lots of people will probably want to see it where ever you go - even to the grocery store. Take the attention as a complement and show it off proudly. Also for that same reason, keep it clean inside!
Keep us all posted on your progress, and you know we will all LOVE to give you advice!!!!!
Enjoy!