Move the rocker switch on the light lens itself to the always on position. It's not obvious but the lens of the light is actually a built in 3 position rocker switch (always off, always on, on when the door is opened) as I recall. Try it out.
This is how the side door and rear door lights work. The front door lights are individually controllable by the grey rocker switch on top of each light but the same 3 positions
"always on" for certain small values of "always" - it will turn off about 20 minutes after the last door open/close event no matter what. I wish there were overrides for that behavior, and for the radio turning off after 20 minutes - I've converted my rig into an RV, and the coach battery gets charged from the house batteries when the engine isn't running, so I don't worry about running the battery down.
I will be changing the 2 factory interior lights to a typical RV light at some point. When I do, I'll figure out the wiring to bypass the timer and switch from van-timed power to aux battery always-on power....shouldn't be too hard.
The radio... now that's another story.. it appears the on off button on the radio is really a button that is connected to the van's computer. When you push the button, it sends a signal to turn the radio on. (timed if the van is not key on) No easy way to power the radio by means of aux battery power....arrrggghhh!
Those lights are being turned off by the CANBUS. If you delete them from the CANBUS circuit it may signal an error. We decided to just leave them and add our lights to the coach battery to avoid any such anguish!