I picked up a few Parkside container wagon kits at Scaleforum and over the last week or 2 I have been putting them together. Along the way a Bachmann example was added too as it was cheap and had the smaller container that I was after.
Above are the Conflats themselves, the 2 on the left being the Parkside ones and the 3rd the Bachmann one. The first one is built as intended with the usual additions of buffers and brake pipes from Lanarkshire models, safety loops from Bill Bedford and tie bar from Eileens emporium. (I’ll come back to the chains in a moment). The second one uses the Red Panda underframes as a lot of those pictured on Paul Bartletts site (link here) seemed to match this configuration. For the Bachmann one it looked a bit of a faff to sort out the underframe as the brakes were set for 00. Strangely Bachmann had the wrong brake levers on either side meaning that the brakes wouldn’t actually work anyway as lowering the lever would pull the shoes even further away from the wheels! A Parkside chassis is the easy option and I had a spare from the second wagon. 
Above is a view of the different underframes. You could go much further than this if you wanted too but this is a representation of what I feel you can see in all the gloom. If you did want to go further then the obvious start point would be one of Justin Newett’s excellent etched chassis but even if you didn’t he puts his instruction on his site anyway and there’s some good references and info on how it should all look. Well worth clicking here! The wagon at the front is the BR clasp underframe. 
I mentioned earlier that I would come back to the chains and to my eye Parkside have been too delicate in the details on this kit. There’s a tendency to think that finer is better but I don’t think it works here. The chain I used is 23 links per inch from Langley models Which as supplied has quite round links with a twist to them. You can see the original shape on the container on the right. To get them to the more lozenge shape it’s simply a case of putting one end of a length of chain in a vice and pulling the other to stretch it. Nothing cleverer than that! The lifting shackles on the roof were also too fine and were replaced with spared from Justin’s Bogie Bolster E underframe detailing kit. In case you are wondering the wagon on the right was destined for the smaller container which is why the raised links are towards the middle. 
The finished wagons – Both large containers were sprayed with Halfords Rover damask red. The apparent difference being due to the weathering. I might be stating the obvious here but it pays to weather the wagons and containers separately meaning the weathering process is earlier in the build than normal. 
The shackles are from Roxey models and use the same Langley chain links. While a little fiddly it does mean that they can be assembled without resorting to the soldering iron! I didn’t use the supplied eyelets for the containers as I felt they didn’t really look much like the prototype pictures I was using so I just used a bit of fine wire instead. Once the chains are in place it worth treating them to a thin coat of ZAP thin CA (the pink bottle) to set everything solid.
I’ve been doing other wagons too. Above a Dia 1/002 Lowfit from the Red Panda kit.
D2109 LMS 16t mineral wagon from the Cambrian kit
A couple of Banana vans – Wrenn bodies on Red Panda underframes with additional details. 
And finally a couple of brake vans – on the left the Airfix kit with Bill Bedford springing and extra details. On the right Hornby RTR.
Some handy links
Parkside Dundas (also for Red Panda)
Eileens Emporium (also for Bill Bedford)