First post:
I just made one last week by mushing together all the threads I read here and everything that was linked. You could find cheaper parts, but I was building mine for a party later that night. Basically I went to the big box store (home depot) and found their only clear housing full house filter ($35 i think), which also has the handy "bypass" switch on top so you can compare randallized and non-randallized beverage. The fittings on the filter housing are 3/4" FPT, home depot only sells pipe thread parts to reduce a single size, so I went with a 3/4" to 1/2" reducer, and a 1/2" to 1/4" reducer, then a 1/4" MPT to 1/4" male flare adapter. (Note: posted in other threads there is a 3/4" to 1/4" reducer and even a 3/4" MPT to 1/4" male flare fitting which can be found online, thus reducing the fittings required and thus the price) My kegerator is setup so every hose is 1/4" flare, making it easy to switch between corny and sanke parts, or in this case, adding an inline randall. The hoses all have 1/4" female flare parts and all hardware (disconnects, randall's, tap shanks) have male flare parts. So all I needed to do was make the randall have 1/4" male flare fittings, and make up a "5' jumper" of beverage line with 1/4" female flares which went between the liquid ball lock disconnect and the randall, the tap side tube was screwed into the out on the randall.
So all my hardware has these fittings:
http://www.northernbrewer.com/brewing/kegging/soda-kegs-fittings/ball-disc-1-4-mfl-gas.html
And all my tubing has these fittings:
http://www.northernbrewer.com/brewing/1-4-barbed-swivel-nut.html
To convert the filter housing, I cut a piece of 1" PVC to 9 and 7/8" to fit inside the housing where the filter once was. I then used a dremel with a disc cutting tool to cut in about 10 parallel slits on each side of the tube on the bottom 1/4 of the tube, to make beer pass through the length of the hops before heading to the tap. These slots worked very well, no clogging and minimal leaf parts exiting to the glass. I'll likely switch to stainless when I get some more time to fuss around with it.
Foaming: Yes, I put the randall inside the fridge on the compressor hump. I have a standard mini-fridge and was still able to fit both corny kegs in as well. The key to not foaming is A) PURGING THE GAS initially when beer is first allowed to flow into the randall using the little pressure relief button on the side of the filter, B) REDUCING YOUR POURING PRESSURE, I turned the tank down to around 8 psi, and C) most importantly 10 FEET OF BEVERAGE TUBING TO THE TAP, this goes for all pouring applications. I had foaming for about 1/2 a pint glass, then nothing but perfect pours all night.
All in all I was amazed at how stupidly easy this was to build and look forward to putting honeycomb in there for a wit!