do you actually notice any extra insulating properties with just the one side and top foam? I would think that the foam would have to be completely around the cooler to add any R-value.
I have not noticed any ice retention difference as yet, mostly cool temps though. Perhaps next summer will tell. I use a soft side cooler when tripping, and with the Solar Bear or DIY dry bag cooler inside the Igloo for transport between the last ice and provisions and a distant put in I figure I am well insulated.
One reason the cooler lives year round in its truck niche, if I am grocery shopping, and making hardware and etc stops, and a diner visit for breakfast on the way home, I put the bag of refrigerated or frozen stuff in the cooler. Even the ice cream is still firm.
The only difference I have found with the additional insulation is that, on chilly nights when my toes poke out from under the sleeping bag, I am not resting them against cold Igloo plastic.
One design fail on the Igloo is the lack of any gasket material between the lid and body of the cooler. That area probably presents the biggest loss of cold retention, and I added thin foam weather stripping to the groove on the lid.
The minicel insulation can not hurt. I added exercise mincel to the top, bottom, front and back.
The truck has a full bed length exercise flooring layer, the thin synthetic truck bed having done nothing for hot or cold prevention in sleeping mode. With a minicel layer on the bottom of the cooler it resting two layers on minicel. The sidewalls of the bed are covered with that exercise flooring as well, so two minicel layers in the back as well.
I did not want to minicel the cooler sides due to the handle recesses and drain hole. In any case the sides of the cooler are sandwiched between a carpeted wood shelf at the front, and the minicel padded tailgate at the back, so there is essentially added insulation surrounding the cooler on those sides as well
That minicel application started out simply as a desire to eliminate that superfluous fish measuring recess and make the top of the cooler lid level. And that mostly because in the summer I rest a nine inch high velocity fan there, aimed to blow gustily from my feet to my head. With the uneven lid top that fan was a wobbly fit.
But, while I had the exercise flooring, contact cement, brush and heat gun out, why not keep going. I even beveled all of the exposed minicel edges.