I don't know about anyone else but I'm not the type of person who likes to proxy models. It just feels wrong. I know that for friendly games it really doesn't matter and I don't mind when other people do it, but I try my hardest not to. So when I decided I wanted to try a Thunderfire out I had two choices. Buy one or build one, and building one was way easier on my wallet. I started with styrene tubing for the individual barrels of the cannon.
I had a barrel piece left over from a Bane Blade/Shadowsword kit I used for housing the barrels. I decided to use tracks, to keep it as close to the real model as possible. The problem was what to attach the tracks to. I found a couple of rectangular sprue pieces that are identical and glued them together making a frame.
I then attached a Razorback back hatch piece to form the base. To the base I added a Landraider engine piece and styrene card for detailing. I destroyed a junk tank kit to get the tracks I used. Small time military model conventions are a great source for cheep parts!
For the cannon its self I started with an old GW paint pot, one of the 2nd ed hexagon shaped ones, and added the Shadowsword/barrel housing piece to the top of it. To connect the cannon to the base I again stole from my Landraider bits. I used sponson uprights turned on the side as the gun's supports.
All mounted to a 25mm base so it would fit into the Razorback hatch piece. I then began to add detail parts to give the model a more complete look. I added the old metal frag launchers from a Landraider Crusader and a sensor module from a new plastic LR kit. As well as plastic card and other bits I felt made the model look complete.
I thought I was done...until I put a model next to it and realized I had completely lost all sense of scale when building the base. I scrambled to find a replacement base idea. I again returned to my Landraider bits. It wasn't until writing this that I realized how many Landraider parts I used! I found a couple of Lascannon bits, using only the half of the Lascannon with holes for the sponson to attach too, I glued them to the tracks. The Lascannon bits worked perfectly to give the model a smaller more compact look. It's still larger than the real thing but I am very happy with the results.