I'm not sure which is easier, trying to build the domed turret or trying to make sponsons that look like the Forge World version seen it the picture there. After my first post on building a turret created a huge amount of feedback and the question was asked about the sponsons, I thought I would give it a go to see what I could do.
I think I was able to capture some aspects, but failed at others. All in all, it might make for a passable model, but it lacks in some respects. I think with a little more work, I might be able to get better results. It's definitely doable.
I started out with a regular chassis. I thought I would see what I could do without any serious conversion work to the model itself. I wanted to limit myself to what I could build or add to a model that was already built. This way, it would be something that someone else could do to an existing model if they wanted to retrofit their own vehicle.
Keeping this in mind, it limited what I could build. I think I managed to make the most of what I had, but I'm sure there are ways to improve on this.
The current door opening is only so wide. This limited me to the width of my new opening since whatever I built would have to fit in that spot. After a bit of back and forth, I decided I would build a new side armour piece that would fit between the two smoke stacks and would allow me to reshape the opening. My first thought was to make my conversion fit inside the current door shape, but this method ending up being easier.
I used a piece of plasticard cut to fit the opening along with a spare 25mm round base and half of a Space Marine bike wheel.
If you look at the Forge World model, it has two things that are key. First is the recessed look to the opening and second is the bulk of the weapon mount. By using the new armour plate and attaching the base and wheel half behind it, I was able to create a similar recessed look.
The weapon mount is where I come up a bit short overall. Mine lacks the bulk the Forge World version has and it's not as substantial looking. If I were to do it again, I would build the mount out of greenstuff so I could get the "bulk" and then cast the pieces so I had enough for both sides of the vehicle.
I think the bulk is a big part of the overall look to the sponsons. Missing it makes the model appear to be lacking in some respects. It still has the feel of it, but not the heft.
And again, priming the parts has a way of bringing out the minor surface flaw, but allows you to look at the piece as a whole.
All in all, I'm happy with the conversion. I've learned a huge amount about working with plasticard between this and the turret I did. I don't know if I'll be adding these to my Predator unless I can get that bulked out look I want to achieve.
Make sure to check out these posts as they might help:
How to build the domed Deimos pattern Predator turret