A big part of the awesome Sludge look is from massive groups of Line Infantry. The multi-miniature bases is such a good idea to get a mass battle look, with quick movement.
I wanted to field two huge groups of Line Infantry. So I've made two full regiments of 6 bases. So that's 12 bases of three miniatures.
My infantry is made almost entirely from Wargames Atlantic WWI French. The box is awesome and comes with 35 miniatures (and 70 gasmask heads). I wanted my army to look uniformed and spend quite a bit of time planning where to use which bits.
All my Line Infantry is armed the same way, there's a few (like three) bodies from Napoleon Elite French, to have enough bodies. All have added toilet paper / super glue cloaks. I've used a mix of backpacks from both the WWI and Napoleon kits. In order to have as many different looks as possible.
The Command bases are the only one to feature conversion work. I've used Perry Miniatures pike arms for the banner flags. The drummers are made with bit box magic. Warhammer bits. A dwarf and empire drum. Drumsticks made from arrow wielding arms. Straps from paper and super glue.
The sergeants are made to look like my Shock Troopers. The have bear pelt hats (a cut and glue job with a wwI head), bucklers, pistols and a different style mask. These come from the ranks of shock troopers and heavy cavalry. So these will all have the same kind of head.