I also agree with your tactics.
I use similar tactics with Thumper.
We used 12 hourly metacam to try to control gut pain for about 6 months, although he's prone to dehydration which is the main risk factor for renal side effects. Subsequent bloods for other reasons showed no abnormality.
My impression was that Thumper had good pain control for 8 hours which would fit with the data.
To reassure you, it seems that most oxicam NSAI's are inactivated in the liver & the
inactive metabolite excreted via the kidney.
http://en.wikipedia.org/wiki/Meloxicam
You've so much to gain by controling pain. There's the kindness aspect, but it will also help the fight against the URI. In rabbits pain causes a marked drop in white cells so they can't fight infection properly, let alone the effect on the gut! Low pain & low stress seems to win the day for bunnies.