I use the big PS (96oz I think) bottle with the proper amount of MMO mixed in (I use about a 3 to 1 mix). I have lines painted on the side and get 4 fill-ups out of the one bottle of mix.

I store it in my bed toolbox in a milk crate along with another gallon of oil (Mobil Delvac 1300), tie downs, welder's gloves, extra drop hitch, and some bungee cords.

Before I installed the toolbox I used an old Mobil 1 oil quart container put into a zip-lock plastic bag behind the back seat. The container did get noticeably thinner after about one month of use.

The way I figure it, if PS comes in a bottle, the bottle should be able to hold it for a while.

 

For my additive use (which comes in a 5 gal pail) I had to find a storage method and preferably a single dose system. The plastic bottles dont work for long I found. I went camping one day and figured why not use some of the stove fuel bottles. They are made of aluminum, seal very well and so far have lasted 3 years and show no signs of wearing out. You can buy them in various sizes depending on your dose needs. I bought 6 of them. Fill them up, toss them in my tool box and pull one out every fill up. I got mine at REI but many stores sell them.