I thought about doing the same thing. I decided on getting a KRL1056 instead to use as a cart. I still like the KRSC46 though. There is also another car you may want to consider. It is a little narrower but it is deeper giving more area and volume in the box, with the same number of drawers. The drawer configuration is different though.
http://store.snapon.com/KRSC246-Ser...teel-Lid-6-drawers-Extreme-Green-P745963.aspx
I think it is a good place to start with a cart. It gives you some time fill what you have and give you something to work with. Then when you outgrow it, you can look for something else. You could buy something used, to save money too. I bought a used Waterloo cart and put my 4 drawer Craftsman rally box on top of that. It has been ok. It is terrible to move around because the castors **** so bad, bud it gave me more space for now and only cost me $50. It about what it is worth tool. The drawer slides on it are not that bad and it is getting loaded up a bit. This combination made it much easier for me to put tools in and out of my box. Before I had to pick up two or three things to pull a tool out. That thing was so packed, the 4 drawer box, It was well over a 100LBs, maybe 150-200. Every time I picked it up I thought the handle might break. I would strap a seat belt around it because I expected the latches to break too. They never did though. I will have that little box back up again in the not too distant future. When I do I think I will weigh it just to see how much it weighs.
The roll carts have lots of add-that allow you customize your cart. There seem to be more options on the carts than on the roll cabinets. The add-ons are also less expensive for the carts than the roll cabs.
Good luck.