I agree with mattsoft.
A slightly cloudy day is better than strong direct sun.
And yes you should reapply every hour to avoid patches.
And definitely wrap in film.
I for a less risky solution buy a clear plastic container at the pound shop and a couple of gallons of 6-7% hydrogen peroxide off eBay and submerge the whole case in it. No atrwaking possible although it may take a couple of days.
I do that for all things up to the size of an ST.
Monitors are a pain as I would need too much fluid so I use a more retrobrite like formula and I still get some blotches, mostly from not following my own advice above.
As an aside, this is generally not a permanent solution.
The keys on my TT keyboard had started to slightly yellow again after just 6 months.
Tests by others indicate that neither sealing doesn't help, neither does lack of light.
It appears temperature may also be a factor depending on the plastic.
I'd advice not coating with anythig, keeping it out of the light when not in use (I use those allegedly UV blocking dust covers) and not keeping it anywhere to warm.
But I'd still expect to have to do it again in a few years at least...
1977 VCS Heavy Sixxer (Boxed)
1990 Atari 1040STE, 4MB, UltraSatan, TOS 2.06, TT Touch -> Atari SC1435 Colour CRT Monitor
1991 Atari TT030, 2/64MB, Int 8GB Gigafile SCSI2CF, TOS 3.06, CaTTamaran Accelerator -> Atari TTM195 19" Mono CRT Monitor
1993 Atari Falcon030, 14MB, Int 4GB IDE2SD, TOS 4.04 -> Atari PTC1426 Color CRT Monitor
Amiga, Mac, DOS, Newton, SGI, Sun, NeXTStation and more!