[CTPJ]

I just filled my two canisters after doing the RV Mod and was able to get just under a 1/4 cubic foot of resin in each one. If you purchase a 1/2 cubic foot resin, you should be fine with a little left over.

Make sure your system produces enough DI water for your needs, so you're not having to replace the resin too often. Depending on the PPM of your water supply and the amount of water you use for each wash, you may be better off with the 20" canisters. I have a flow meter on my system and I typically use around 10 gal of DI water per wash. This is only using it for the foam canon and the final rinse. I'm running an Active 2.0 pressure washer that flows at 1.9 GPM.