2002 Express intermittent dead battery

Have a 2002 Express 3500, 5.7, single rears, passenger van body.

Having an issue where it's intermittently draining the battery. Latest example: battery was near-dead (dim dome light) on a Friday. Checked for charging & draw, OK. Replaced battery with a new one. Van started with no problems on Saturday and was driven a short while. Van sat Sunday, and battery was completely drained on Monday.

Charging system is working normally, and am getting NO current draw with ignition off (or at least the electronics are drawing under 1/10th of an amp). Checked wiring harness in various places looking for abrasion & shorts, found nothing. Door switches & dome light appear to be working correctly.

Problem seems to be more apparent in our recent Siberian weather.

Any second opinions on this?? Thanks in advance. :)

Amp draw should not be over .025 milliamp draw after computers power down.

Hook up amp draw tester and watch for a couple hrs.

In case of sometimes dead try unhooking battery over weekend and see if it goes dead unhooked.
If so you have a bad/bad battery.
If not you have a drain/draw some place.
And check battery voltage when parking it.