Just wanted to share how i'm going about this.
Decided i wanted a K2 Catapult, because i got enough plastic Catapults as it is and it is more fitting model for the Free Rasalhague forces i'm planning.
I don't have existing bits for guns, missile launchers and so on, and i can't currently get IWM parts, so i have to craft the PPCs. In this case, i took the tube/straw thing from used compressed air can that is about 3mm in diameter. The Alpha Strike Lance Pack plastic Catapult's missile launchers are about 5mm by 5mm, so it should look reasonable.
What i've done so far:
-Cut a piece of tube, aiming for about 10mm.
-Drill a wide-ish hole to the launcher, and a deeper smaller one inside for a pin. I don't have 3mm drill bit so i have to improvise.
-One end of the PPC tube gets squeezed with pliers to flatten it a bit and some excess cut to make it somewhat triangular to fit better the too small hole in the launcher.
-Going to use a pin to make sure the thing stays in there.
Once the PPC barrels are in place, i'm going to add some greenstuff inside the front end to make a concave paintable surface, and i'm also going to use greenstuff to smooth out the launcher to barrel transition and hide the ugly mess the drill caused.
I figure once this is all done, after priming and painting it should look fine, right?