Sounds like a good solution for you. You probably have the water jugs and other things in a tote or something so they will not slide around, spill, pick up POL vapors, etc.

My vehicle presents a harsher environment, and not just in terms of apparently harsher winters. Items like stove, fuel, water, and 3 days food are stowed in an aluminum tool chest that sits across the bed rails behind the cab (4x4 pick up). Tool chest is pretty full of other useful things that are for the most part heavy, sharp, or both as compared to milk jugs.

While I try to avoid stowing potential missiles in the cab, the Ready pack (no water in the wintertime) and fanny pack of additional first aid supplies are in the cab (rear seat area and clipped in when I remember to do that). I DO carry water in the cab on trips, but M-F my daily commute is less than 8 miles round trip.

We use empty milk jugs primarily for two things. Oldest (for us) use is backpacking (except wintertime). We each carry an empty partially collapsed one gallon jug on the outside of our packs. When we stop in the evenings, these are filled with potable water, along with our regular water containers. Supper, breakfast, clean-up, and minor personal hygiene are readily handled out of that water without needing to make additional trips to whatever water source we are using. By the end of a week long trip, some may develop a pinhole leak or two, but a scrap of duct tape or electrical tape takes are of that.

A couple of years ago I had one of those forehead thumping moments and made a slight improvement. Using a carpet needle, I threaded some braided dacron fishing line thru the caps and with a fisherman's knot, made the line into a loop. The loop gets girth-hitched to the jug handle and the cap never gets misplaced or lost (Yeah - only took me 30 years to think of that). At the end of the trip, the jug is tossed in the recycle bin and the cap goes in a baggie and back in the pack or personal gear tote. Certain fastidious people seem to feel better with a little dab of food-grade silicon caulk on the inside of the cap over the two holes and thread, but I don't bother. I got carried away with the idea and made up, oh, several lifetimes worth of "tether able" caps - both snap on and threaded types.

The other main use we make of empty milk jugs is simpler. My DW keeps the thermal mass of our chest-type freezer constant by adding jugs of water as the food contents fall. That really extends the time between generator runs when the power goes out for more than 24 hours (main reason), plus if we are using a cooler on the road portion of a trip, she uses a frozen jug or two in the ice chest.

But my tool chest would be an extremely lethal environment for milk jugs. As I wrote previously, I intend to try out a couple of those Guyot water bottles this year.

Regards,

Tom