Leaving drainplugs open (even partially) can have catastrophic effects on the longevity of your ice in hot climates. Hot air gets in there and will melt your ice near the drainplug. Last Grand trip I was on was March-April. It was a frigid trip. I had a cooler that had only a block of sculpture-grade ice in it. Even with the cool temps (our hottest day was probably low 70s), by midway I noticed a large bulge of melt space in the side of the block centered on the drainplug. I checked it, and the plug had been left open a day or two prior.
As far as inside drainplugs- sounds cute, but how do you get to it without rearranging and/or partially unpacking it? Seems like you'd lose so much cold having the lid open so long. Also, seems like more work than just lifting the cooler out of the bay and draining normally.
I'm the one on our trips that ends up having to be the cooler-nazi. It's not always pleasant or convenient, but I've kept ice for 15 days on the river of a 16 day Grand trip in July plus a couple of days drive down (coolest daytime high was probably 95+ with temps in the 110s regularly). Another long trip, Deerlodge Park to Hite, we had ice left at the takeout after 15 days on the river, plus 3 days before we put-in. Highs on that trip were probably upper 90s every day.
Point is just that every little thing you do (or don't do) will really affect the life of your ice. Rules for keeping ice for 2+ weeks:
a. Don't open your cooler. If you have to get food out, wait until the sun goes down, or at least it gets cooler outside. Get breakfast going early, before the sun hits the cooler.
b. Keep your cooler shaded. I like to put a paco pad on the coolers all day long. Better to sit on, too.
c. Keep a burlap sack wet and drape it over the cooler, under the paco pad. At 115 degrees, you'll be soaking your burlap at least every hour during the day.
d. Drain your cooler DAILY.
e. Use sculpture grade ice if you can get your hands on it. It's circulated during freezing, leaving it void of air bubbles. Brined ice, that you can get in blocks melts MUCH more quickly than sculpture ice.
f. Pack your coolers completely full, and shoot for having no more than 1/2 the volume of the "frozen" cooler taken up by food, the rest of the space for ice. Produce cooler can have more food, and less ice.
g. DON'T OPEN THE COOLERS!
By the way, in the Denver area I've been really happy with Aesthetic Ice
. Craig was easy to work with and gave me a really good deal.